Re: dagger?

I have a sneaking suspicion that dagger categories might be of interest in some work I'm doing, but the term means absolutely nothing to me. Category with involution does have a meaning, which is why I think they might be interesting. Could someone please post a definition of a dagger category and a reference for typical useful examples? For other examples of a notations promoted to the name of a concept: K theory, L functions, p matrices, H spaces (OK, that one is a bit of a cheat, since it comes from the first letter of a name instead of from the arbitrary choice of symbol), \lambda calculus. Lawrence Stout Professof of Mathematics Illinois Wesleyan University