For purposes of whether you can claim your child as a dependent, "disabled" means "permanently and totally disabled." Here's the definition of permanently and totally disabled from IRS Publication 501.
Permanently and totally disabled. Your child is permanently and totally disabled if both of the following apply.
- He or she can't engage in any substantial gainful activity because of a physical or mental condition.
- A doctor determines the condition has lasted or can be expected to last continuously for at least a year or can lead to death.
But again, this would only apply to someone who is 19 years old or older. If he is under 19 it doesn't matter whether he is disabled or not.
