Recent testing revealed that Arch Linux, Pop!_OS, and even Nobara Linux, which is maintained by a single developer, all outstripped Windows for the performance crown on Windows-native games. The testing was run at the high-end of quality settings, and Valve's Proton was used to run Windows games on Linux.
It’s how long it takes the system to render the next frame. High frame times are no good. Equates to lower average fps, and poor player experience. You also want stable frame times. This equates to smooth gameplay and less “stuttering”. Anything under 20ms is considered good. 10ms and less is great. Anything over 50ms will be perceived by the player in a negative way.