Minority group - People who are singled  out for unequal treatment  and who regard  themselves as objects of  collective discrimination.
Ethnicity - A shared identity based on  cultural elements such as  heritage, language, and  religion.
Majority group - A group's subset that  consists of more than half  of the entire group's  members.
Race - A socially constructed  group of people who share  physical characteristics  that are considered  significant by a society  and that are used to  distinguish them from  other groups.
Explanation:
To better understand the above-mentioned definitions we would use some examples:
Elder people can be considered as a minority group in the United States because of their reduced status as a consequence of popular discrimination and prejudice against them. In contrast to them, young men consisting of more than half the population in the age category is an example of the majority group.
Groups of people like Hispanic Americans, Jews, Italian America, Irish are some examples of people belonging to different ethnic backgrounds residing in the U.S.
African Americans who are distinguished based on their skin color is an example of race.