What is program collision?/Can a namespace prevent collisions?

I've done some google searches for just what program collision is and how to prev开发者_开发百科ent it with no results for C# or even a generic answer. I'm thinking collisions would be if one variable has the same name as another or possibly 2 classes with the same name on accident.

He was just talking about when two variables have the same name or two classes. That's all. -_-'