Question

What exactly is acting??

Answer 1

Being someone else, you're given a role & for once in your life you can be someone who is completely different from you. 

Although if its on life situations its pretending to be.

ex. Stop acting stupid.
You're likely to be joking around.

hope it helps.

Answer 2

I think acting is the ability to make another believe what you say and do. To act is to provoke a deeper emotion in someone. If you can act out a feeling and make someone else feel it, you are a good actor/actress.  

I hope this helped you :)