Edge servers terminate TLS, cache static assets, route requests, and absorb spike traffic so the origin doesn't have to. CDNs (Cloudflare, Fastly, Bunny) operate networks of edge servers.
For a tunnel service, the "edge" is the public-IP server that accepts inbound traffic and forwards it to the agent on your laptop. lrok's edge is a single Hetzner box in Helsinki — single-region but cheap, which is why we can charge $9/mo flat. ngrok and Cloudflare Tunnel run multi-region.
Latency-wise, single-region Helsinki adds ~30-50ms RTT in EU, ~80-180ms US-East-to-Helsinki. For webhook testing and OAuth callbacks, that's invisible. For real-time low-latency interaction, you'd want a regional edge close to the user.