Hello
A KUID is simply a Serial Number of an Object.
While an object can have the same name as another, it's KUID is unique within the game.
Every User has his own KUID Range if he plans to upload content, which can be viewed in your Planet Auran Profile under "Your User ID".
Mine is 46012 for example, so if I was going to upload a layout, it's KUID might be <KUID:46012:1000> for example.
The Content Creation Guide, which can be downloaded from the TRS Website, has more detailled Informations regarding KUIDs (and lots of other stuff too).
I hope that helped a bit.
Tata
Mr.Jingles