SEO Glossary: Key Terms Explained

How to Use This Reference

Every field develops its own language, and search is no exception. The terms collected here are not jargon for its own sake, each one names a real concept that explains something about how search engines work, why they behave the way they do, or how people interact with them. Understanding what a term means is different from knowing how to use a tool that measures it. This glossary focuses on the former.

Terms are grouped by theme so that related ideas sit together. Reading a cluster in sequence often reveals how the concepts reinforce one another. Where a term connects to a broader principle covered elsewhere in the course, that connection is noted.

Search Fundamentals

Search Engine

A system that indexes content from the web, interprets queries, and returns ranked results it believes best satisfy what the searcher is trying to accomplish. The core challenge a search engine solves is matching language (the query) to meaning (the intent behind it).

Query

The words or phrase a person types or speaks into a search engine. A query is a signal of intent, but it is an imperfect one, the same words can mean different things to different people in different contexts.

Search Intent

The underlying goal a person has when they enter a query. Search engines classify intent into broad categories: informational (wanting to learn), navigational (wanting to reach a specific destination), commercial (wanting to compare options before deciding), and transactional (wanting to complete an action). Understanding search intent is the foundation of why content either satisfies or frustrates a searcher.

SERP (Search Engine Results Page)

The page a search engine returns after processing a query. SERPs are not static lists of ten blue links, they are dynamic compositions that may include organic results, paid advertisements, featured snippets, image carousels, video results, local packs, and knowledge panels. The composition reflects what the search engine believes will best serve the intent behind the query.

Organic Result

A listing on a SERP that appears because the search engine's algorithm determined it to be relevant and trustworthy, not because the publisher paid for placement. Organic results are earned through relevance, authority, and quality signals over time.

Algorithm

The set of rules, signals, and machine-learning models a search engine uses to decide which pages to surface and in what order. Algorithms are not static; they are continuously updated as search engines learn more about what satisfies searchers.

Crawling and Indexing

Crawler (Spider / Bot)

An automated program that systematically browses the web by following links from page to page. Crawlers discover content so that search engines can evaluate and index it. Without a crawler visiting a page, that page cannot appear in search results.

Crawlability

The degree to which a search engine's crawler can access and navigate a website. Pages that are blocked by technical directives, hidden behind login walls, or unreachable through broken links cannot be crawled, and therefore cannot be indexed. Crawlability and site architecture are closely linked because the structure of a site determines which paths a crawler can follow.

Indexing

The process by which a search engine stores and organizes content it has crawled so that it can be retrieved quickly when a relevant query is made. Being indexed is a prerequisite for appearing in search results, but indexing alone does not determine ranking.

Index

The search engine's database of crawled and processed content. When someone searches, the engine queries its index rather than the live web. The index is vast but not exhaustive, not every page on the internet is included.

Robots.txt

A text file at the root of a website that communicates instructions to crawlers about which parts of the site they are permitted to access. It is a convention, not an enforced technical barrier, well-behaved crawlers respect it, but it does not prevent all bots from accessing content.

Canonical Tag

An HTML element that signals to search engines which version of a page should be treated as the definitive one when duplicate or near-duplicate versions exist at different URLs. It helps search engines consolidate signals rather than split them across multiple versions of the same content.

Relevance and Ranking

Relevance

The degree to which a page's content matches the meaning and intent behind a query. Relevance is not simply about keyword matching, it encompasses topical depth, content structure, and how well the page addresses the specific question or need the searcher has.

Keyword

A word or phrase that represents a topic or query. In the context of search, keywords are the bridge between what people type and what content exists. The significance of a keyword lies in what it reveals about intent, not in how many times it appears on a page.

Semantic Search

An approach to search that attempts to understand the meaning behind a query rather than treating it as a string of individual words. Semantic search allows engines to connect a query to relevant content even when the exact words used in the query do not appear in the content.

E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness)

A framework Google uses in its quality evaluation guidelines to assess whether content demonstrates genuine knowledge and credibility. It reflects the understanding that not all content is created equal, content written from real experience by recognized experts on authoritative sites tends to serve searchers better than thin or unverified content.

Featured Snippet

A highlighted answer extracted from a web page and displayed prominently at the top of a SERP, above the standard organic results. Search engines surface featured snippets when they believe a specific portion of a page directly and concisely answers the query.

Core Web Vitals

A set of metrics that measure the quality of a user's experience loading and interacting with a page, specifically loading speed, visual stability, and responsiveness to input. These metrics matter to search engines because a poor experience signals that a page may not genuinely serve users well, regardless of its content quality.

Authority and Links

Backlink

A hyperlink from one website pointing to another. Search engines interpret backlinks as signals of endorsement, when a credible, relevant site links to a page, it suggests that page has value worth referencing. The quality and relevance of linking sites matters far more than the raw number of backlinks.

Domain Authority (DA)

A third-party metric (not a Google metric) that estimates the overall strength of a website's backlink profile on a scale from 1 to 100. It is a proxy for trustworthiness and influence, not a direct ranking factor, but it reflects the kind of accumulated credibility that does influence how search engines perceive a site.

PageRank

Google's original algorithm for measuring the importance of a page based on the quantity and quality of links pointing to it. The underlying principle (that links act as votes and that votes from important pages carry more weight) remains central to how search engines evaluate authority, even as the algorithm has evolved considerably.

Internal Link

A hyperlink that connects one page on a website to another page on the same website. Internal links serve two purposes simultaneously: they help crawlers discover and navigate content, and they distribute authority signals across the site. Internal linking strategy reflects an understanding of how information architecture shapes both crawlability and relevance.

Anchor Text

The visible, clickable text of a hyperlink. Anchor text provides context to both users and search engines about what the linked page contains. Descriptive anchor text that reflects the topic of the destination page is more informative than generic phrases.

Link Equity (Link Juice)

The value or authority that passes from one page to another through a hyperlink. Not all links pass equal equity, links from highly authoritative pages on relevant topics pass more value than links from low-quality or unrelated sources.

On-Page Structure

Title Tag

An HTML element that specifies the title of a web page. It appears as the clickable headline in search results and as the tab label in a browser. Title tags are one of the clearest signals to search engines about what a page is about.

Meta Description

A short summary of a page's content that may appear beneath the title tag in search results. It does not directly influence ranking, but it influences whether a searcher chooses to click, making it a factor in how well a page performs in practice.

Heading Tags (H1–H6)

HTML elements that define the hierarchical structure of content on a page. An H1 typically represents the primary topic of the page; H2 and H3 tags organize subtopics beneath it. Clear heading structure helps both search engines and readers understand the organization and scope of content.

Schema Markup

Structured data added to a page's HTML that helps search engines understand the type and meaning of content, for example, whether a page describes a recipe, an event, a product, or a review. Schema can enable rich results in SERPs, such as star ratings or event dates displayed directly in the listing.

URL Structure

The format and composition of a web page's address. Clear, descriptive URLs that reflect the topic and hierarchy of a page are easier for both users and crawlers to interpret than opaque strings of numbers or parameters.

Understanding the Bigger Picture

These terms do not exist in isolation. Each one names a piece of a connected system, a system built around the fundamental challenge of matching what people want to find with content that genuinely serves that need. Search engines evolved because that challenge is hard, and the vocabulary of SEO evolved as practitioners tried to understand and work within the rules those engines established.

Knowing what these terms mean is the beginning of understanding why search works the way it does. The deeper knowledge comes from seeing how the concepts interact: how intent shapes relevance, how relevance depends on structure, how structure is discovered through crawlability, and how authority is built through trust signals over time. That interconnection is what makes search a system rather than a collection of isolated features.