SEO Glossary: Essential Definitions 2026
SEO has a dense technical vocabulary that can seem opaque to marketing teams new to organic search. This glossary defines the fundamental terms used in link building strategy, SEO audits, and ranking tracking — with a focus on concepts related to backlinks and domain authority.
- Authority metrics (DR, DA, PageRank)
- Link types (backlink, nofollow, guest post, niche edit)
- Technical vocabulary (crawl, indexation, SERP, anchor text)
- Referring domain and link profile concepts
Backlink
A hyperlink from an external site pointing to a page on your domain. Backlinks are one of Google's primary trust and authority signals used to rank pages in search results.
Domain Rating (DR)
A proprietary Ahrefs metric (0–100) that evaluates a domain's overall authority based on the quantity and quality of its inbound backlinks. A high DR generally correlates with stronger ranking ability, but real organic traffic is an essential complementary indicator.
Domain Authority (DA)
The equivalent of DR but developed by Moz. Expressed on a 0–100 scale, it models the likelihood that a domain will rank in SERPs. DA and DR measure similar things but their algorithms differ — a site can have DR 60 and DA 45.
Anchor Text
The visible, clickable text of a hyperlink. Google uses anchor text to understand the thematic context of the linked page. A natural distribution includes branded, generic (click here), topical, and exact-match anchors. A profile dominated by commercial exact-match anchors is a manipulation signal.
PageRank
Google's original algorithm (Larry Page, 1998) that measures the importance of a web page based on the number and quality of links pointing to it. While Google stopped displaying public PageRank in 2016, the algorithm continues to operate internally in an evolved form.
Nofollow
A link attribute (rel="nofollow") that instructs search engine crawlers not to follow the link or transfer authority. Introduced in 2005 to combat spam, it evolved in 2019 with two new attributes: rel="sponsored" (commercial links) and rel="ugc" (user-generated content).
SERP
Search Engine Results Page — the page displayed by a search engine in response to a query. Modern SERPs include organic results, featured snippets, People Also Ask, Knowledge Panels, local results, and paid ads.
Crawl
The process by which Googlebot (Google's crawler) explores the web by following links to discover and revisit web pages. Crawl frequency for a page depends on its authority, content update frequency, and the crawl budget allocated to the domain.
Indexation
The addition of a web page to Google's database after Googlebot has crawled it and deemed it eligible. An indexed page can appear in search results. Pages can be excluded from indexation via the meta robots noindex tag or the robots.txt file.
Referring Domain
A unique domain that contains at least one backlink pointing to your site. The number of referring domains is a more significant indicator than total backlink count — 100 links from 100 different domains carry more value than 100 links from the same domain.
Guest Post
An article written by an external author and published on a third-party site, typically including a link back to the author's site. Guest posts are a common link building practice — Google tolerates it when content delivers genuine value to readers, but penalises large-scale guest post networks with thin content.
Niche Edit
A link building technique that inserts a link into an existing, already-published article on a third-party site. Also called a link insertion or curated link. The value of a niche edit comes from the authority already accumulated by the existing page — a link in a page that ranks and drives traffic transfers more authority than a link in a new article.
Apply these concepts in a tailored link building campaign.
Explore Orbink ServicesFrequently asked questions
What is the difference between DR and DA?
DR (Domain Rating) is an Ahrefs metric and DA (Domain Authority) is a Moz metric. Both measure domain authority based on backlink profiles, but their algorithms differ. Neither is an official Google metric — they are third-party approximations. To evaluate a site, always cross-check these metrics with real organic traffic (Ahrefs, Semrush) and domain age.
Is a nofollow link completely useless for SEO?
No. Google stated in 2019 that it treats nofollow as a "hint" rather than a strict directive, meaning some nofollow links may transfer authority. Additionally, nofollow links on high-traffic media generate direct visits and reinforce brand signals — two factors that indirectly influence SEO.
How many backlinks do I need to rank on the first page?
There is no universal answer. The number of backlinks required depends on keyword competitiveness, authority of competitors on page one, and link quality (topical relevance, DR of the referring domain). In a low-competition niche, 10–20 quality backlinks may suffice. In competitive iGaming or crypto, top-ranking sites often have thousands of referring domains.
This glossary is complemented by two additional resources: the Advanced SEO Glossary for in-depth technical concepts, and the Google Penalties & Algorithms Guide to understand the updates that affect rankings.