1) A sign of approval.
2) Also a insult equal to the middle finger in some cultures (namely the middle eastern ones, where you saw pics of iraqi children giving the thumbs up to american soilders)

An action with the hands that used to be used solely an expression of agreement or acceptance, but when used as an emoji on social media can now also mean "I'm pleased for you, but don't want to carry on the conversation" - a polite version of "whatever" - a way of saying 'whatever' but pretending that you liked what they said.

Traditionally denotes well wishes though could also imply taking a rest from celting

Something next to my definition that you really oughta click

Giving someone the “thumbs up” hand gesture or emoji, is another way to say “fuck you”

While popularly used as the term for approval (thumb's down for disapproval ) Not many know that in rap or in Fighting word's thumb's up means safety off due to the motion of taking the safety off is putting your thumb's up.

The beginning to most YouTube comments.