An equilibrium is a self-perpetuating situation that does not change, even when a force for change is introduced from the outside that alters the basic data describing the situation.

Ceteris paribus is an assumption used in economic models in which the important variables that you are focusing on are kept constant.

In economics, a model is a simplified representation (diagrammatical or physical) that helps us to understand what is going on by focusing attention on what is important.

An economic rent is the benefit you receive above what you would have earned from your reservation option.