edit:
https://developer.valvesoftware.com/wiki/Counter-Strike#Vers...
Also custom maps are mods by definitions anyways, with the exception of games where the creation of maps is a component of gameplay.
Or, if you were slightly older, you might call them UMS, as they were in Starcraft. Short for "Use Map Settings", indicating that the game logic should come from the scripts and triggers in the map file rather than the built-in logic for ladder games.
This is even better. Because it's a map you can start it without modifying your game installation.
There were "real" WC3 mods, but it was always cumbersome and worked reliably only in singleplayer.
Gameplay-wise it's a mod obviously.