Option Select is a term for doing one or a group of commands that will do different actions depending on what the opponent chooses to do. These can take on many forms and can be very simple or complex, universal or character specific. We will go over a few examples.
Throw Option Select Example
A simple example is the throw option select in Guilty Gear. A throw in Guilty Gear is done by pressing Template:6
. Button priority in Guilty Gear goes (Throw and 
> 
> 
> 
> ), which means doing a command like Template:6 means your character will do Throw if the opponent is in range (and not throw invincible) or Template:6 if the opponent can not be thrown. The game is selecting which option to do for you depending on the situation!
Reverse DP Input Example
A slightly more complex example is a reverse dp input to deal with crossups: Ragna
Options selects are a