Gotcha means "I've got you" and is a slang expression. I would use gotcha if I was playing games with children and I had to catch them. We can also say gotcha when another person falls for a prank. I tell my friend that today is my birthday and they believe me, but in fact it isn't my birthday. I would say gotcha when they finally realise it isn't my birthday.

Gotcha means I got it or I got u. It's similar to I understand u.

It's shortened slang for 'I got you', or 'caught you.'

I think gotcha is relaxed pronunciations of ''got you''.Gotcha is meaning to comprehend, i guess :)