TTFB (time-to-first-byte)

RU: TTFB (время до первого байта)

Time To First Byte: the elapsed time from a browser sending an HTTP request to receiving the first byte of the response. It combines network round-trip latency plus server processing time and is a foundational metric because every subsequent paint metric (FCP, LCP) cannot begin before TTFB completes. A target of under 800 ms is considered good by web.dev guidelines.