Checkmate in 1/2 move

what is 1/2 move

how do you make 1/2 of a move??  are you like not allowed to do a castle that puts someone in check?  are you allowed to make half a castle if this is the case?  and also, wouldn't king to H2 checkmate him?  i don't see the magic in this puzzle.....

I don't get it but kh2 is the answer

Funny

I really dont get it... Could someone explain it to me?

This half-moves, joke puzzle etcera look really stupid to me, but it's just a personal opion anyway

The white king was in the middle of castling?  I thought it was Kh2 as well, can someone explain please...

It's a joke. Like this:

When you castle short/long in chess, your king moves two squares towards either rooks and then the rook sits to the opposite side
the joke here is that the king moved two squares, but the rook still haven't moved to his side yet which is the second part of the castling process. that's where the "half a move" comes from.

There was checkmate