The term second coming refers to Jesus’ return to Earth at the end of time, leading up to the judgement of all mankind. His first coming, of course, was as a human baby. His second coming will be His return as conquering king and judge. Nobody knows when this will happen.
I'd like to personally challenge Mr. Camping to act with integrity on May 22, 2011. On that date, it will be refreshing to hear him publicly and undeniably say that he was wrong. I've extended the same challenge to other would-be prophets with little success, so I'm not going to hold my breath.