A minority group is any group of people who does not get equal access to power, wealth, and resources compared to a dominant group (majority group) based on its cultural and physical differences. A minority group consists of characteristics such as race, ethnicity, religion, gender, sex, and disabilities. The characteristics of a minor group’s definition do not take into account its number, i.e., it may prevail in population over the dominant group.
For example, we can see in the U.S. that women get less paid than men though “in 2017 there were 165.92 million women […], compared to 159.41 million men.” 
Speaking about a personal experience, during 1920-1991, Ukrainians lost political power on their land with the advent of communist forces, where the largest group become a minority group and had limited access to the social institutions. To get a high-paying job in the public sector (government, education, military, or medicine), Ukrainians had to reject their identity and language to become a part of the dominant group. Otherwise, they could only work on collective farms.
Considering people with disabilities, in some societies, they do not treat equally as other groups, including other minorities, so they often get discriminated in terms of their physical or mental disabilities. Because of that, they do not get comfortable use of restroom facilities, elevators, or any other physical objects. I am happy that many efforts have been made in the U.S. to improve the living experience of this minority group.