When two things in the same (relatively broad) grouping have the same name.

Take the WandGroup network engineers (WAND) at Waikato University and the WanDaemon software (WAND) developed by a couple of people who worked there.

Derived from programming:

A namespace is much what it sounds like - a finite space that names can be defined and identified in. For example, if you're writing a program and you wanted to define a class called Object, you'd be out of luck as the class Object already exists. If you were able to define a second class called Object, how would the computer know the difference between the two?
Namespace collision
When two companies/groups/people try to name thier classes with the same name, or define methods off of a class with the same name. To help avoid namespace collision not only within your own projects, but from other companies like third party vendors, it's a common practice to prefix your classes with some acronym, for example, if you work for !MegaCorp? you might prefix all your classes with 'Mc'

See also: NameSpace.