It's an informal term originating in the US which means different things to different people.
There is no universal agreement on what the term means and never will be; it was originally used in the US to mean 'awareness of injustice' but it has since gained negative connotations as the term has been used to describe extremist behaviour by far left extremists and the term is often used in a derogatory manner. When I hear the term, it is generally used negatively to describe behaviour of people when trying to cancel something or complain about something (such as the
LNER announcement fiasco).
It is probably best to avoid the use of the term, as people on different 'sides' will have completely different ideas as to what the term means; if you asked 10 people, you would probably get 10 different answers. It is a divisive matter, that's for sure.