Meta tags live in the HTML <head> section and serve three core functions: communicating with search engines, controlling browser behavior, and defining social media presentation. For search engines, the title tag and meta description remain the primary signals. The title tag (technically not a meta tag but grouped with them) directly impacts rankings and appears as the blue clickable link in search results. The meta description doesn't affect rankings but influences click-through rate, which indirectly matters for traffic. Google rewrites descriptions roughly 70% of the time, but you still need to provide one that targets your primary keyword and gives users a reason to click. The robots meta tag controls indexing behavior. Using "noindex" keeps pages out of search results without requiring server-level blocks. The canonical tag prevents duplicate content issues by telling Google which version of similar pages to prioritize. These matter significantly for e-commerce sites with filter URLs or agencies like Ottawa SEO managing 500+ domains where technical control prevents indexing chaos. Viewport meta tags make pages mobile-responsive by telling browsers how to scale content on different screen sizes. Since Google's mobile-first indexing, this shifts from nice-to-have to mandatory. A missing or misconfigured viewport tag means your site renders poorly on phones, killing both user experience and rankings. Open Graph and Twitter Card meta tags control how content appears when shared on social platforms. Without them, Facebook and LinkedIn pull random images and text. With them, you control the thumbnail, headline, and description, which directly impacts social click-through rates. We see clients neglect meta tags in two ways: either stuffing keywords into descriptions thinking it boosts rankings (it doesn't), or ignoring them entirely and letting Google auto-generate terrible snippets. The practical middle ground is writing concise, benefit-focused descriptions under 155 characters and ensuring technical tags like canonical and viewport are present and correct. Check these in batches using Screaming Frog rather than manually reviewing every page.