Wiktionary
n. A period of time during which a person is absent from work or other duty for a reason other than normal holidays / vacation; may be paid or unpaid.
WordNet
n. the period of time during which you are absent from work or duty; "a ten day's leave to visit his mother" [syn: leave]
Wikipedia
A leave of absence (LOA) is a period of time that one must be away from one's primary job, while maintaining the status of employee. This contrasts with normal periods away from the workplace, such as vacations, holidays, hiatuses, sabbaticals, and "working from home" programs, in that they are considered exceptional circumstances, rather than benefits. Generally such an arrangement has a predefined termination at a particular date or after a certain event has occurred.