An enemy pawn can serve as an umbrella: it blocks the file along which the defending rook would like to check, so the attacking king can escort its own pawn in peace.
White wants to promote the e-pawn, and Black's rook on f1 is ready to check along the f-file. But look at the black pawn on f4: it stands between the rook and the white king on f5. The pawn is Black's own piece, and it is exactly what shelters the white king. This is the umbrella.