The word "handicap" is often used interchangeably with "disability"  However, the two words do not have the same meaning.

Disability is a condition caused by an accident, trauma, genetics, or disease which may limit a person's mobility, vision, speech, or cognitive function.

Handicap is a physical or attitudinal constraint that is imposed upon a person, regardless of whether that person has a disability.

Example:  Some people with disabilities use wheelchairs.  Stairs, narrow doorways, and curbs are handicaps imposed upon people with disabilities who use wheelchairs.