From BRWiki
A province is a medium geographical region that is regarded as a single political or cultural unit. Normally the regent (if any) in control of a province as its head-of-state is the one who has the greatest law holdings within its borders and has been invested as the province's regent. A regent can control multiple provinces as part of their domain or realm, directly or through vassalage.
Provinces are described by their terrain and by their level. The terrain effects movement, adventuring, and imposes limits on the maximum level that a province can reach. The level describes the prosperity, organization, importance, and population of a province. There is also a source potential level for most provinces. This restricts the number and power of the source holdings. Provinces are normally described by the numbers M/N, where M is the province level and N is the maximum number of source holdings.
See Also: Components of a domain: Provinces - the BRCS section describing provinces in depth
