The term "gentile" does not appear in the original text of the Old Testament or anywhere in the Bible; it is a word translators added. Stemming from the Hebrew word "goy," "gentile" roughly means "tribe" or "nation." It the bible, "goy" was translated to mean "nation" or "gentiles," depending on the interests and influence of those in power. Often times, the term "gentile" was used in translations to set clear boundaries between Jews and non-Jews.
In some of the earliest books of the Old Testament, the term "gentile" was used to refer to all of those who came from Noah. The Bible depicts Noah building an ark right before a worldwide flood, where he saved two of each species of animal. After the flood, Noah repopulated the Earth, and all of his descendants were called gentiles. Thus, in biblical terms, all humans were gentiles for a period of time.
Later in the Bible, "gentile" was used to denote differences among people. Specifically, the term was at first used to describe all early people in the Bible, possibly because they all had a universal "nation" or system of beliefs. When Jesus Christ surfaces in the gospels, the term began to be used to denote differences between those who believed in the sanctity of Christ and those who did not. This led to the use of "gentile" as a descriptor for non-Jews, or those who followed Christ.
Mormons, who belong to the LDS church, use the word "gentile" to refer to all non-Mormans or all of those who do not share their Mormon beliefs. This is seemingly contradictory because Jews refer to Mormons as gentiles. The Book of Mormon represents the primary text for Mormons, and it is said to have three authors: Jews, Lamanites and gentiles. This description suggests that the Mormon faith differentiates between general gentiles and Jews.