The ISO 3166-2 codes for Sweden describe the 21 Counties, or län. The first part is the ISO 3166-1 code SE, the second part of the code, which is used domestically, is alphabetic 1 digit, except three cases which are 2 digit. The ordering is based on a geographical "path" starting in Stockholm and then clockwise the counties of southern Sweden and finally the northern counties.
The purpose of this family of standards is to establish a worldwide series of short abbreviations for places, for use on package labels, containers and such. Anywhere where a short alphanumeric code can serve to clearly indicate a location in a more convenient and less ambiguous form than the full place name. US readers may wish to consider them as the equivalent of worldwide zip or postal codes. Within the Wikipedia, the codes from the country pages link to the pages for the locations they identify.