What does plush mean in a mattress?

Plush means a soft mattress feel: a thick, cushioned comfort layer that lets the body sink in rather than rest on top, typically rated around 3 to 4 on the 1 to 10 firmness scale.

A plush mattress cradles the hips and shoulders, which is why side sleepers tend to prefer it. Back and stomach sleepers usually need medium to firm support to keep the spine aligned. Plush is a manufacturer label, so one brand's plush can feel firmer than another's.

Plush mattress firmness typically falls around 3 to 4 on the 1 to 10 scale.
Most side sleepers prefer soft to medium mattresses, which includes plush models.
Most back and stomach sleepers prefer medium to firm mattresses, not plush ones.
The industry medium-firm standard sits around 6 to 6.5, well above plush.
Plush feel comes from a thick comfort layer of memory foam, latex, or poly foam.