Meaning of “firm” - Learner’s Dictionary

firm

adjective uk us /fɜːm/
NOT SOFT

B2 not soft, but not completely hard:

A firm bed is better for your back.
FIXED [ always before noun ]

B2 certain or fixed and not likely to change:

We don't have any firm plans for the weekend yet.
I'm a firm believer in equal rights.
STRONG

strong and tight:

a firm handshake/grip
STRICT

strict and making certain that people do what you want:

You've got to be firm with children.
firmly adverb
firmness noun [ U ]

(Definition of “firm adjective” from the Cambridge Learner’s Dictionary © Cambridge University Press)