new to hi lo

Back Means  you are going against computer prediction

Lay Means You are going with computer prediction gonna be happen

lay means to rest money down and back and back means to lay back or guess you won't win. I guessed computer wins and I win.

I think Jazza has hit the nail on the head there.
When you lay the computer prediction you back each possible result.
So obviously if you want to back each losing result you would have to lay back each winning selection.

Riveting stuff.