A piece of functionality that is producing unexpected output (or exhibiting unexpected behaviour) given certain input. Expected behaviour is defined by spec if available, or by the developer in the absence of such. Finally it comes down to the customer to decicde what is "expected".

The related items has been confirmed as valid/correct by an appropriate person

Ongoing development issues. Usually these should be tied to a milestone.

Items that require discussion by some parties.

Items relating to documentation in some way.

Items that will improve or extend the existing system in someway. Examples: new functionality, better UI, better docs

Items that relate and/or impacts security in anyway