Many people who can't get in to MSA call it summer school or nerd camp, but they don't know what they're missing.
In the USA this refers to an urban cluster (continuously built up area,) or clusters of 50K people of more each, the county it (or they) sit in, as well as the counties (or townships in New England) where significant numbers of people commute to and from that county. It includes urban (high density,) suburban (lower density,) and exurban (rural nonfarm) areas, as well as farmland.
Definition: Geographical divisions, determined by the United States Office of Management and Budget, for the purposes of census data and other urban population calculations. The divisions are primarily based on urban areas, and tend to follow town or county borders. The MSAs can also be broken down into smaller “Metropolitan Divisions.” Previously called Standard Metropolitan Statistical Area (SMSA).