Meta tags live inside your HTML <head> and convey page metadata to search engines, browsers, and social platforms. They don't appear in visible content but directly affect how your page ranks, displays in search results, and renders across devices. The core meta tags every page needs are the title tag (technically not a meta tag but often grouped with them), meta description for the SERP snippet, and viewport for mobile rendering. Beyond that, robots meta controls indexing and crawling behavior, canonical tells Google which URL is the master version when you have duplicates, and Open Graph plus Twitter Card tags shape how links display when shared on social. You'll also see charset (UTF-8 for character encoding), author, and generator tags, but those matter far less for SEO. Older tags like meta keywords haven't been used by Google since 2009 and just bloat your code. The practical hierarchy at Ottawa SEO: title and meta description get written for every page, viewport is mandatory in the template, canonical goes on anything with URL parameters or pagination, and robots meta only appears when we need noindex or nofollow on specific pages like thank-you forms or staging content. We skip meta keywords entirely. Common mistakes include stuffing the description with keywords (Google often rewrites it anyway), forgetting viewport (kills mobile rankings), and setting conflicting signals between robots meta and robots.txt. Also watch for CMS plugins that auto-generate redundant or contradictory tags, especially on WordPress installs with multiple SEO plugins active. One nuanced point: Google may ignore your meta description if it doesn't match search intent for a given query, pulling text from the page body instead. That's not a failure of the tag, it's the algorithm deciding what snippet best answers the user. Write descriptions for clicks, not just for the sake of having one. If you're seeing 60-character truncations in SERPs, you're over the roughly 155-character mobile limit Google uses now.