When the instructor assesses you for Skipper Small Keelboat or Skipper Large Keelboat competence after training, you will be assigned a competence grade. But perhaps you are maybe not quite as competent as you should be to reach the Skipper Competence grade - 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 sailing Skipper ranks, not power skipper rank or any Bareboat Charter Ranks
You can gain more experience to get more skills on your own or with the Instructor/assessor. The instructor/assessor can reassess you later and remove the provisional restriction.