The care and support of your child - which means that you can use it for pretty much anything, clothing, shelter, utilities, food, or anything else specifically for the child. I don't know that it's actually designated from a legal standpoint though. It's just the money that is supposed to help the primary caregiver make sure that the child's needs are properly met.
It's there to help support the child, clothing food etc. If a person is getting child support they can use it however they see fit though. As long as it isn't for anything illegal. You can't get mad at your ex and sue them because they made a car payment or bought a television with the money you gave them seeing as it typically goes into their bank account with the rest of their money.