Networking
Head-of-Line Blocking
One delayed item stalls everything queued behind it. In TCP, a lost packet blocks all bytes after it.
Why interviewers ask about it
Why HTTP/2 can be slower than HTTP/1.1 on lossy networks, and the reason QUIC moved reliability above UDP so streams are independently ordered.
Related terms
This term is part of the free System Design interview preparation module - browse the full glossary for every definition.