CS 1.6 Resolved Query

So I don't know if this is Ok to ask but I have been thinking what's the need of those first words before "_" in map names like de_dust2, what's the need of "de" and what does it mean. Many other maps like cs_assault, what's the need of "cs" in it?

It indicates the type of game mode those maps are used for, de_ is for defusal, cs_ is for hostage rescue, aim_ is for killing without an objective etc. It's not needed and we could rename the maps to dust2, office, assault etc., but these abbreviations are used since the game release and were used for 20+ years, so there is no point in changing what developers made and what players are used to.