From Academic Kids
Absolute majority is a supermajoritarian voting requirement which is stricter than a simple majority. It means that more than half of all the members of a group, including those absent and those present but not voting, must vote in favour of a proposition in order for that proposition to be passed.
As an example, let's say that a member of a club of 100 members proposes a new bylaw. According to the club's practice, for the bylaw to pass, it requires an absolute majority. The results of the vote are 40 yes votes and 30 no votes. The rest of the voters either abstained or did not vote. Even though this arrangement is a simple majority, since an absolute majority for the club is 51 members, the proposed bylaw fails.
Absolute majority voting is most often used to pass changes to constitutions or to bylaws in order to ensure that there is affirmative support for a proposal. Most voting decisions require a simple majority or even just a plurality.
Examples of absolute majority voting
From 2005, an absolute majority of the electorate in addition to a three-fourths vote of the legislature is necessary to pass amendments to the Constitution of the Republic of China on Taiwan as well as to ratify a referendum. The requirement of an absolute majority rather than a simple majority effectively gives both major political blocs the power to veto a referendum or constitutional amendment.
In the politics of the European Union, any decision taken using the codecision procedure requires an absolute majority in European Parliament in order to amend a text in its second reading. (At first reading, only a simple majority is required.)