The term Mormons is a term given to people who believe in the divine nature of The Book of Mormon, and are members of The Church of Jesus Christ of Latter-day Saints or one of the many smaller organizations that have separated themselves from the Church.
Members of the various Mormon churches may prefer to be called by the official name of their church; but the term is useful to collectively describe all those groups which derive from Joseph Smith. Sometimes "Restoration Churches" is used for this purpose instead, but that can lead to confusion, since there are an entirely different group of Christian churches (those derived from Campbell, e.g. the Church of Christ) who are also called "Restoration Churches".
Some scholars (e.g. Melton, in his Encyclopedia of American Religion) further subdivide the Mormons into "Utah Mormons" and "Missouri Mormons". The Missouri Mormons are those Mormons who did not travel westward to Utah, and the churches formed from them (the RLDS, Strangites, Temple Lot, etc.); whilst the Utah Mormons are those Mormons who did travel westward to Utah, and the churches formed from them (the LDS church, the various polygamy-practising churches.) This nomenclature is not common within the church.