Handicapped vs. Disabled

Some may use these terms interchangeably. Handicapped vs. Disabled. Is there a difference? Is one politically correct?

Here's what Villanova University has to say about this matter:

A disability is a condition caused by an accident, trauma, genetics or disease which may limit a person’s mobility, hearing, vision, speech or mental function. Some people have more than one disability.

A handicap is physical or attitudinal constraint that is imposed upon a person, regardless of whether that person has a disability. A set a stairs would be a handicap for a person with a disability who uses a wheelchair.