A pad is a soft cushion or mat that protects or supports something. Football players wear pads to keep their bodies from being injured, and you may sit on a pad to cushion your bottom.
A thick cotton bandage is one kind of pad, and your mattress might be topped by another kind of pad. There's also the the soft, cushion-like pad on the bottom of an animal's paws as well as the fleshy part of your own fingertips. There are numerous other pads, including ink pads and helicopter landing pads, and — informally — your cool apartment, or pad. When you pad something, you stuff it, cushion it, or fill it out.