It's a high five that doesn't involve actually contact, normally over a long distance where a real high-five isn't possible.

Mix of "wireless" and "high-five", hence "wi-five", (wireless high-five)
> Iain (yelling across the room): Dude, that mess was teh pwnz. Wi-five, brosef
> Eric (in response): You need to chill with that [nano] shit, son