What Is A Windows Registry Cleaner?

I like to think that I know quite a bit about computers. No, I can’t build them, but I can install cards and software and solve problems for people who have gotten a computer virus or two (or fifty!). I can even reformat and reinstall Windows XP. However, mention a phrase like windows xp registry cleaner and I’m ready to run for the hills! The only registries I’m familiar with are bridal registries. I don’t have a clue what a computer-related registry cleaner is. And I don’t think I want to know. Just contemplating it makes my head ache and I want to run out for the biggest bottle of ibuprofen available at the drug store.