Majority means the greater number of something. The opposite is minority.
If more than half the people are right-handed we can say that the majority of people are right-handed. A minority of people are left-handed. In fact, nearly everyone is right-handed, so we can say that the "vast majority" are right-handed, and only a "small minority" are left-handed.
If a political party or candidate gets a majority of votes, it means that they get more than all the other parties. In Plurality voting, they only get more than any one of the others. Thus if there are three parties, the winning party may have a plurality of 40% while the other two each have 30%. A "true majority" or "absolute majority" means more votes than all the other parties together, i.e. more than half the total votes.
Majority Facts for Kids. Kiddle Encyclopedia.