An option select (shortened OS) is a technique where the player performs a set sequence of inputs that will give different results depending on the situation or the action done by your opponent. The game "selects" automatically for the player the outcome and ensures therefore that the player will always end up in a safe or favorable situation. As such, OS circumvent the need of guessing what your opponent will do next. Because of the way they work, the presence of OS during a match is usually hidden to the viewer or the opponent outside of very specific situations as it looks like the player is always correctly reading the opponent and reacting accordingly.
Option selects are generally exploits of specific properties or bugs of the game engine where it has to decide for ambiguous situations. Their presence is often unavoidable without removing or limiting other positive features of the engine such as input leniency. While games like Street Fighter V are designed to limit as much as possible the number of OS in order to encourage reading, some other games like Guilty Gear Xrd actively support the use of OS by displaying them in training mode.
Example: in Street Fighter IV, the so-called crouch tech OS was done by holding down-back and pressing LP+LK at the end of the blockstun while being pressured. This could result in three different outcomes:
- if the opponent pressed another button, the player would block it;
- if the opponent tried to throw the player would tech the throw;
- if the opponent stopped and did nothing else, due to how the game engine gave priority to kick buttons when kick and punch buttons where simultaneously pressed the character would perform a cr. LK and hit the opponent or force him to block.
While historically the terms option select and buffering were interchangeable, the former is now used for series of inputs that are always performed without waiting for any visual cue to confirm the inputs.