According to the search results, an Eskimo sister is a slang term that refers to two women who have shared a sexual partner and are on friendly terms. The term is similar to "Eskimo brothers," which refers to two men who have slept with the same woman. The term "Eskimo" may have originated from a custom in Alaska of "reciprocal spouse exchange, sometimes described as co-marriage," according to the Straight Dope. However, the term can be considered offensive in Canada, so some sources suggest using alternative terms like "Pogo Sisters".