A compressor turns down signal above a threshold by a set ratio, then lets it recover. Gentle compression makes vocals and instruments sit steadily in a mix; heavy compression creates a punchy, aggressive sound.
Limiters are extreme compressors used at the end of mastering to prevent peaks from clipping.
Using it in a prompt
Words like "punchy", "squashed" or "pumping" tend to imply heavy compression; "natural" and "open" imply light compression.