TTFB is the time taken between the point an API call is made to the moment the client receives the first byte.

Lower TTFBs result in better UX.

The metrics is often used in server-side rendering designs. Server-side renders have longer TTFBs than client-side renders because HTML is compiled at the server-side.

It can also serves as an indicator of network latency.

Enabling caching, using a CDN (content delivery network), optimising database queries, and reducing HTTP requests can reduce TTFB.