What is the fork?

The fork is an attack on 2 pieces and only one of them can escape eg see below.
Thanks evryone and be sure to check out the link below!
https://www.youtube.com/watch?v=dl8QE-M89FY
Technically 5. b5 is also a fork. Only one of them can escape in a given turn (bu running or capturing the pawn).

thank you it is very useful post for me especially the link , but daniel rensch explained the knight fork only he didt talk about the others forks types he mentioned .
i mean he didt talk about the pawn forks and tempo forks in this video

The fork is an attack on 2 pieces and only one of them can escape
So, by that definition, is this a fork?

The fork is an attack on 2 pieces and only one of them can escape
So, by that definition, is this a fork?
That’s a pun.

The fork is an attack on 2 pieces and only one of them can escape
So, by that definition, is this a fork?
pin.

The fork is an attack on 2 pieces and only one of them can escape
@batgirl is making the point that this description is not a definition of a fork because it also describes a pin.

The fork is an attack on 2 pieces and only one of them can escape
@batgirl is making the point that this description is not a definition of a fork because it also describes a pin.
A Fork attacks two (or more) pieces simultaneously. A Pin or a Skewer attacks two or more pieces sequentially.