"Administration Level 1" is the generic term for the largest subnational administrative unit of a country. This unit has different names depending on the country: for example, "state" in the USA and "prefecture" in Japan. In this data.frame the country name is in the column "admin" and the admin1 region name is in the column "region". Rather than working with this object directly, consider using the helper functions listed below.
This map is too large to efficiently render by itself with ggplot2. You should subset it by country before attempting to render. Please see the helper functions.
Taken from http://www.naturalearthdata.com/downloads/10m-cultural-vectors/10m-admin-1-states-provinces/. This is version 3.0.0 of the map and is considered to be beta. The wikipedia page on "Administrative division": http://en.wikipedia.org/wiki/Administrative_division