Apron

From PinWiki

The apron is a metal (or in early games, wooden) covering that comprises the lower boundary of the playfield. On most machines the apron holds the instruction and pricing cards, as well as covering the ball trough and shooter lane. Many aprons have a credit lamp on the left side which indicates that unused credits remain on the game. The rear-facing side of the apron is generally shaped to guide balls to the center drain once they fall past the flippers or out the outlanes.