The OSR extension is specific to files created by a video game called Osu! An OSR is a file used to store a video clip with a record of the gameplay. It is often referred to as the replay file.

Osu! is a game of clicking on the screen in the right places to the rhythm of the music being played. OSR files contain all information about the game such as time, score, player's nickname. Such replays are often mentioned by game users.