A treaty is a formally concluded agreement between parties. Think of parties as the groups involved--typically individual countries. In the previous century, treaties were often thought of as agreements between just two parties (two countries signing a peace treaty, for instance). But in today’s world, a treaty is often a multilateral agreement, meaning it is signed by three or more parties. Treaties are legally binding once signed by a party.
The word convention is often used interchangeably with treaty, but there are slight differences between the two. A convention is a special type of agreement between a large number of countries. Imagine the word convene, which means come together. In a convention, countries come together to discuss a global issue and reach a consensus about the procedures they should take in response. Unlike treaties, conventions are not necessarily legally binding, and they can act more as frameworks or concepts that do not include specific measures.
Protocols are similar to treaties, but they generally amend, supplement, or clarify an agreement.
One key term is also Article 5 and non-Article 5 parties. Under the Convention and the Protocol, we do not use the terms developed and developing.