Autorun
Autorun is a mechanism for making running scripts alongside maps easier.
Modfile autorun
Mod autorun is a ModuleScript inside the mod itself called "autorun" that runs when the mod is loaded. You can see an example mod in the mod list.
VIP server autorun
Server autorun is the autorun tabs inside the private server console. The server autorun runs when the VIP server starts letting you load a map without having to join yourself after the server restarts and the client autorun runs per-client.