To identify the odd one out among the options, let's analyze each term:
The terms Gazelle, Antelope, and Stag all refer to types of wild, hoofed mammals, typically found in open or wooded areas, often grouped together based on similar habitats and characteristics. The term Mare, however, refers specifically to a particular gender of a domesticated animal, the horse.
Thus, the odd one out is Mare, as it differs by representing a domesticated animal and specifies gender, unlike the others, which are types of wildlife animals.