Wax
Also known as: skate wax
Wax applied to ledges and rails to cut friction so you can slide.
Extended definition
Wax is skate wax (a stick or block) you rub on edges, walls and rails so the board and trucks slide instead of catching. Waxing a ledge well can turn an unusable spot into a perfect one, which is why it's part of every street skater's kit. Too much wax, on the other hand, leaves it slick and dangerous for whoever comes after.