What does "White is down a rook for a pawn" mean? I am not a native English speaker and I'm learning to play online chess.
I often find a sentence with this pattern.

White is down a rook for a pawn.

What does it mean? Could you elaborate on this sentence and make it much more understandable for me?
It means that white is down a rook, and up a pawn compared to black. So black has one more rook than white, and white has one more pawn than black