"The Clap" is a common name for a sexually transmitted infection called Gonorrhea. Gonorrhea is caused by a bacteria and you get it by having vaginal, anal or oral sex without using a condom.
This is really pretty nasty yet I believe that "having the clap/s" or "The claps" is when someone has an std-I think it's Gonorrhea or something similar. I know it relates to this anyway... Yuk, I...