Just to add a term: the name for this kind of behaviour is aliasing. Which is a concept that people seem to have little trouble using in practice, but much harder to understand and explain. Some languages have no concept of aliasing at all. In perl @_ is aliased, as are the iterator in a foreach loop, grep, map and sort. In Pascal "var" parameters are essentially aliases, as are normal parameters in VB (byref parameters). Its my understanding that C has no aliases.

I find a useful way of thinking about aliases is that they are like references that need not be dereferenced.