It's a leather ball (now they make them out of rubber too) that is packed solid. They usually come in weights of 9, 12, 15 lbs., or larger. You can do drills with it by yourself or do partner drills. I like doing the partner drills, you go with the three minute timer and toss the ball back and forth. There are various ways to toss it, from back behind the head, like a volley ball (as soon as it hits your hands you push it back to your partner) and one hand throws. It's also a good ab developed when you have your parnter throw it at your midsection.