Difference between PID and TID

Question

What is the difference between PID and TID?

The standard answer would be that PID is for processes while TID is for threads. However, I have seen that some commands

Answer 1

Just to add to other answers, according to man gettid:

The thread ID returned by this call is not the same thing as a POSIX thread ID (i.e., the opaque value returned by pthread_self(3)).

So there are two different things one could mean by TID!