What is a tight loop?

From Wiktionary:

1. (computing) In assembly languages, a loop which contains few instructions and iterates many times.
2. (computing) Such a loop which heavily uses I/O or processing resources, failing to adequately share them with other programs running in the operating system.

For case 1 it is probably like

for (unsigned int i = 0; i < 0xffffffff; ++ i) {}

A tight loop is a loop that loops many times and the loop body has few instructions.