A
- Anchor Text
- The visible, clickable text of a hyperlink. Search engines use anchor text as one signal for the destination page's topic, so descriptive anchors ("how to fix 404 errors") perform better than generic ones ("click here").
- Authoritative Domain
- A domain with strong reputation signals — Wikipedia, government sites, major news organisations. Outbound links to authoritative domains rot less often and provide stronger citation value than links to small, unknown sites.
B
- Backlink
- A link from another site pointing to yours. The most important external signal for SEO. When backlinks point to URLs that 404, the link equity is lost.
- Broken Link
- A hyperlink whose destination returns an error (404, 5xx, connection failure) or never resolves. Internal broken links are entirely your responsibility; external broken links are unavoidable but need to be managed.
C
- Canonical URL
- The single preferred URL for a piece of content, declared via
<link rel="canonical">. Tells search engines which version to index when multiple URLs serve the same content.
- Connection Timeout
- The destination server didn't respond within a reasonable window. Functionally equivalent to a 404 from the visitor's perspective; usually transient but persistent timeouts indicate a server problem.
- Crawl Budget
- The number of URLs a search engine bot will crawl on your site in a given period. Wasted on broken links, redirect chains, and orphaned pages instead of new content.
- Crawler
- A bot that systematically reads pages from a website by following links. Search engines (Googlebot, Bingbot) crawl to build their indexes; SEO tools crawl to audit.
D
- DNS Lookup
- Translating a domain name (example.com) to an IP address. If DNS fails for a destination, the link is effectively dead even if the underlying server is fine.
E
- External Link
- A hyperlink from your site to a different domain. Subject to link rot beyond your control.
H
- HEAD Request
- An HTTP method that returns response headers but no body. Useful for link checking because it's lighter than a full GET. Some servers reject HEAD requests, requiring a fallback to GET.
- HTTP Status Code
- A three-digit number in the response indicating the request's outcome. 2xx = success, 3xx = redirect, 4xx = client error (broken link), 5xx = server error. See our full reference.
I
- Internal Link
- A hyperlink from one page on your site to another page on the same site. Your responsibility entirely; broken internal links are always avoidable.
- Index (Search Engine)
- The database of URLs a search engine knows about and may show in results. URLs that 404 or 410 get dropped; URLs behind redirects get replaced by the redirect target.
L
- Link Depth
- The minimum number of clicks from the homepage to reach a given page. Pages at depth 4+ are crawled less often by search engines and harder for users to discover.
- Link Equity (Link Juice)
- The ranking value passed from one page to another via a hyperlink. Preserved through 301 redirects, lost through 404s, partially lost through 302s and chains.
- Link Rot
- The gradual decay of hyperlinks as their destinations disappear, change ownership, or change purpose. Affects external links inevitably; can affect internal links if not maintained.
M
- Meta Refresh
- A redirect implemented via
<meta http-equiv="refresh"> in HTML rather than HTTP status. Search engines may treat as a 301 or as a soft 404 depending on timing. Use server-side redirects instead.
N
- Nofollow
- A link attribute (
rel="nofollow") telling search engines not to pass link equity to the destination. Originally for spam control; now also used for sponsored and user-generated content (rel="sponsored", rel="ugc").
O
- Orphan Page
- A page that exists on your site but has no internal links pointing to it. Reachable only via direct URL or external sources. Search engines may not find or re-crawl them.
- Outbound Link
- A link from your site to another domain. Same as external link.
P
- Permalink
- A URL designed to remain unchanged for the lifetime of the page. WordPress permalinks are the canonical example. Permalinks should never need to redirect — that's the whole point.
R
- Redirect Chain
- A sequence of two or more redirects in a row before reaching the final URL. Adds latency, wastes crawl budget, and dilutes link equity. See our guide.
- Redirect Loop
- A cycle of redirects (A → B → A) that never resolves. Browsers detect and stop with
ERR_TOO_MANY_REDIRECTS. Almost always a configuration bug.
- Redirect Map
- A list (typically a spreadsheet) of every old URL and its corresponding new destination. The single most important artifact in a website migration.
- Robots.txt
- A file at
/robots.txt telling crawlers which URLs to skip. Doesn't prevent indexing on its own; needs to be paired with the noindex meta tag for that.
S
- SAN List
- Subject Alternative Name list in an SSL certificate. A link to an HTTPS URL whose hostname isn't in the certificate's SAN will fail with an SSL error in the browser. Common after a domain change where the cert wasn't reissued to cover the new hostname.
- Sitemap
- An XML file listing the canonical URLs on your site. Submitted to search engines via
/sitemap.xml and Google Search Console. Should never list URLs that redirect or 404.
- Soft 404
- A page that returns HTTP 200 (success) but has no real content — typically a "not found" template that didn't set the right status code. Worse than a real 404; see our guide.
- SSL Error
- Failure of the HTTPS handshake — typically expired certificate, untrusted issuer, or hostname mismatch. The link technically exists but browsers refuse to load it.
T
- Trailing Slash
- The
/ at the end of a URL. /page and /page/ are technically different URLs to many servers. Pick one canonical form and redirect the other to it.
U
- URL Inspection (Search Console)
- A Google Search Console tool that shows how Googlebot sees a specific URL, including its index status and any redirects encountered. Critical post-migration verification.
W
- Wayback Machine
- The Internet Archive's snapshot service at
web.archive.org. Stores historical versions of public web pages. The standard fallback for citing pages that no longer exist.
Common mix-ups we keep seeing
- 301 vs 302
- This is the single most common terminology mistake we see in audit conversations. 301 is permanent, 302 is temporary. A 302 used for a permanent move silently destroys SEO value because search engines never transfer ranking signals through it. If you're not certain which one is configured, scan the affected URLs and check the response codes — don't trust the CMS dashboard's label.
- Broken link vs broken page
- A "broken link" is the source-side problem: a hyperlink on your page that points somewhere dead. A "broken page" is the destination-side problem: a URL on your site that returns an error. The fix is different for each. Broken links are fixed by editing the source page; broken pages are fixed by restoring content or setting up a redirect.
- 404 vs 410
- Both mean "the page doesn't exist," but 410 is a deliberate "won't be back." Search engines drop 410'd URLs from their index faster than 404s. Most CMSs serve 404 even when 410 would be more accurate. We rarely see 410 in the wild outside of intentional cleanup work.
- Redirect chain vs redirect loop
- A chain is multiple hops in sequence (A → B → C → final). A loop is hops that cycle back on themselves (A → B → A). Chains slow down page loads and dilute equity; loops cause infinite redirects that browsers eventually give up on. Both are bugs, but loops are more visible and more urgent.
- Soft 404 vs hard 404
- A hard 404 is honest — the server returns the 404 status code. A soft 404 is dishonest — the server returns 200 OK but the page says "not found" or has no real content. Search engines treat soft 404s worse than hard 404s because they signal a poorly configured site rather than just a missing page.
- Nofollow vs noindex
- Nofollow tells crawlers not to follow a specific link. Noindex tells crawlers not to add a specific page to their index. They're independent settings — a page can be nofollow but not noindex, or vice versa. Misapplying noindex when nofollow was intended is a common mistake during SEO experiments.
- Internal link vs external link
- Internal: same domain. External: different domain. Subdomain handling is the gotcha —
www.example.com and blog.example.com are treated as different domains by some tools and the same domain by others, depending on the eTLD+1 rule being used. When in doubt, treat subdomains as external for link audit purposes.