Amendment

An amendment is a formal or official change made to a law, contract, constitution, or other legal document. It is based on the verb to amend, which means to change. Amendments can add, remove, or update parts of these agreements. They are often used when it is better to change the document than to write a new one.
Contracts.
Contracts are often amended when the market changes. For example, a contract to deliver something to a customer once a month can be amended if the customer wants it delivered once a week. Usually, everyone involved in the contract must agree to the amendment before it goes into effect. Most contracts are written with rules about amendments, like if they are allowed, who must agree to them, and when they go into effect. 
Constitutions.
Constitutions are often amended when people change their minds about what the government should do. Some of the most famous constitutional amendments are the First Amendment to the United States Constitution which added the freedom of speech, religion, press, and protest, and the Third Amendment to the Constitution of Ireland, which let Ireland join the European Union. Constitutional amendments usually must be approved by both the parliament or legislature and a referendum - a vote by all citizens in a country.
Motion.
In parliamentary procedure, the way that many meetings are run, an amendment is a type of motion - a proposal or formal suggestion to do something. Amendments can remove words, add words, or change words from motions. Usually, any motion can be amended, even other amendments. However, an amendment to an amendment of an amendment is often not allowed.