The term 'minority group' has different usages depending on the context. According to its common usage, a minority group can simply be understood in terms of demographic sizes within a population: i.e. a group in society with the least number of individuals is therefore the 'minority'. However, in terms of sociology, economics, and politics; a demographic which takes up the smallest fraction of the population is not necessarily the 'minority'. In the academic context, 'minority' and 'majority' groups are more appropriately understood in terms of hierarchical power structures. For example, in South Africa during Apartheid, white Europeans held virtually all social, economic, and political power over black Africans. For this reason, black Africans are the 'minority group', despite the fact that they outnumber white Europeans in South Africa. This is why academics more frequently use the term 'minority group' to refer to a category of people who experience relative disadvantage as compared to members of a dominant social group. To address this ambiguity, Harris Mylonas has proposed the term 'non-core group' instead of 'minority group' to "refer to any aggregation of individuals that is perceived as an unassimilated ethnic group (on a linguistic, religious, physical, or ideological basis) by the ruling political elite of a country" and reserves the term 'minority' only for groups that have been granted minority rights by their state of residence.

Minority group membership is typically based on differences in observable characteristics or practices, such as: ethnicity (ethnic minority), race (racial minority), religion (religious minority), sexual orientation (sexual minority), or disability. The framework of intersectionality can be used to recognize that an individual may simultaneously hold membership in multiple minority groups (e.g. both a racial and religious minority). Likewise, individuals may also be part of a minority group in regard to some characteristics, but part of a dominant group in regard to others.

The term "minority group" often occurs within the discourse of civil rights and collective rights, as members of minority groups are prone to differential treatment in the countries and societies in which they live. Minority group members often face discrimination in multiple areas of social life, including housing, employment, healthcare, and education, among others. While discrimination may be committed by individuals, it may also occur through structural inequalities, in which rights and opportunities are not equally accessible to all. The language of minority rights is often used to discuss laws designed to protect minority groups from discrimination and afford them equal social status to the dominant group.