When the instructor assesses you for competence after training, you will be assigned a competence grade. But perhaps you are maybe not quite as competent as you should be - but close enough to be safe. In that case you may be given a provisional restriction.
For example, perhaps you are a great skipper in everything except stronger winds. In that case, your instructor may sign you off as a skipper but place a provisional restriction on you such as cleared for no more than 12 knots of wind - or perhaps no more than 2 miles offshore.
Provisional restrictions are attached only to Skipper rank.