Originally published in 2015, updated for 2026. This glossary keeps the timeless fundamentals, retires the dead buzzwords, and explains how AI-driven search interprets these concepts today. Use it as a quick reference, or to remember what “LSI” meant back when people still said “Web 2.0”.
Modern SEO & Marketing Terms
- AI SEO: The integration of AI tools for keyword discovery, content optimisation, and SERP analysis. In 2026, it’s how most marketers actually do SEO day-to-day.
- Algorithm Update: A change to a search engine’s ranking system. Usually followed by panic, Twitter threads, and sudden “SEO expert” activity.
- CRO (Conversion Rate Optimisation): The process of improving a site or landing page to increase the percentage of visitors who take action, whether that’s a purchase, form fill, or call.
- CTR (Click-Through Rate): The ratio of users who click your result versus those who just see it. A sign of relevance, curiosity, or occasionally, misleading meta titles.
- Core Web Vitals: Google’s user experience metrics focused on load time, responsiveness, and layout stability. Basically, make your site faster and stop things jumping around.
- Entity SEO: Optimising around people, brands, and concepts rather than just keywords. The key to being recognised by AI models as a “known source.”
- E-E-A-T: Experience, Expertise, Authoritativeness, and Trust. A framework Google uses to gauge whether you actually know what you’re talking about.
- Featured Snippet: The zero-click box that “steals” your content to answer a question directly in search. Great exposure, questionable reward.
- PMax (Performance Max): A Google Ads campaign type that uses machine learning to optimise across all ad formats. Wonderful and terrifying in equal measure.
- Schema Markup: Structured data added to your pages to help search engines understand what’s on them. Think of it as subtitles for your website.
- Search Generative Experience (SGE): Google’s AI-powered search preview that summarises results in a chat-like interface. Your content either fuels it or vanishes beneath it.
- UX (User Experience): The overall feel of using a website. Bad UX means nobody converts; good UX means they don’t even notice how easy it was.
Obsolete or Retired Terms (RIP, SEO 2010s)
- LSI (Latent Semantic Indexing): A once-popular myth suggesting Google uses LSI to understand content. It doesn’t. Never did. Still won’t.
- PageRank Toolbar: The little green bar that ruined friendships and agencies in the early 2010s. Gone, but not forgotten.
- MFA (Made For AdSense): Low-quality sites designed purely for ad clicks. Modern equivalents are AI spam blogs. Same idea, new disguise.
- Keyword Density: The percentage of times a keyword appears in your text. Long considered irrelevant, yet somehow still mentioned by 2005-era SEOs.
- Google+: Google’s attempt at social networking. Let’s move on.
HTTP Status Codes (and What They Mean for SEO)
- 200 OK: Everything’s fine. Your server is happy. Google is happy.
- 301 Moved Permanently: A permanent redirect. Passes almost all ranking value. Use this for domain changes and fixed URL structures.
- 302 Found (Temporary Redirect): Temporary redirect. Doesn’t always pass authority. Avoid unless truly temporary.
- 307 Temporary Redirect: A more modern version of 302 that preserves method. Google treats it as temporary, too.
- 404 Not Found: Broken page. Happens. Just make sure it’s intentional and serves a helpful 404 template.
- 410 Gone: Tells Google the page is permanently gone. Good for expired content you’ll never bring back.
- 429 Too Many Requests: Your server is throttling crawlers. Often a sign you need caching or a better host.
- 451 Unavailable for Legal Reasons: Used for blocked or removed content. Yes, it’s named after Fahrenheit 451.
- 503 Service Unavailable: Server overload or maintenance mode. Use it sparingly and don’t let Google think you’ve died.
Final Word
SEO terminology evolves fast. Ten years ago it was “backlinks and meta tags”. Today it’s “entities and generative AI”. Tomorrow, who knows? Keep this glossary handy, keep your site fast, and keep your definitions short.
