To mess about is to waste time in a silly way. Not working, and not really playing either.
It is thoroughly British and thoroughly informal. There is a second and sharper sense, since to mess about somebody means wasting their time and changing plans repeatedly, which is a real complaint about a company or a person. And there is a lovely gentle use from a children's book about messing about in boats, which means doing something pleasant with no purpose at all.
1phrasemess aboutTo waste time doing nothing useful.
“Do not mess about — we leave in ten minutes.”
2phrasetreatTo treat somebody inconsiderately by changing plans.
“They will mess about anybody who does not complain.”
Also accepted in games: mess around
Practised in Phrasal Verbs, A Man Called Ove
First appears in chapter 7 of A Man Called Ove.
Practise this word