Definition
First Byte
The time it takes for the browser to receive the first byte of the server response.
Definition
First byte, often called TTFB, measures the time from requesting a resource to receiving the first byte back from the server.
Meaning
It reflects server, network, DNS, connection, and backend processing delays before the page can really start loading.
Why It Matters
A high first-byte time can slow every other performance metric and may point to hosting, caching, backend, or network issues.
History And Context
TTFB became a common diagnostic metric as web performance tools started separating server response time from browser rendering time.