Edge computing runs your application code at CDN points of presence (PoPs) distributed globally, instead of at a single centralised origin server. When a user in Tokyo hits your API, it runs in Tokyo — not in Virginia.
Benefits: dramatically lower latency (10-50ms vs 200-500ms round-trips), higher throughput, better resilience. Trade-offs: constrained runtime environments (no full Node.js), tight limits on memory, execution time, and package size, and different data-locality considerations.
Major platforms: Cloudflare Workers (V8 isolates), Vercel Edge Functions, Deno Deploy, Fastly Compute@Edge, AWS Lambda@Edge. Edge is now standard for authentication middleware, personalisation, geolocation, A/B testing, and any latency-sensitive endpoint.