A figure of speech is an expression whose words are not used in their literal meaning.
- He has a few skeletons in the cupboard.
(He doesn’t literally have skeletons in his cupboard. It means he has a few secrets.)
- I have a million things to do.
(I have many things on my ‘to do’ list. Not literally a million.)
- You are driving me up the wall.
(It means you are annoying me.)