The OMB defines a core-based statistical area (commonly referred to as a CBSA) as "a statistical geographic entity consisting of the county or counties (or county-equivalents) associated with at least one core of at least 10,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties with the counties containing the core."
The OMB delineates a core-based statistical area as "a statistical geographic unit comprising counties (or equivalents) with at least 10,000 inhabitants and adjacent areas linked by strong commuting relationships."