Constraint (mathematics)

condition of an optimization problem that the solution must satisfy

When looking at a mathematical problem to solve, there are two kinds of conditions, possible solutions must satisfy: The first kind of condition is directly linked to the problem description, and can be derived from it. There's a second kind of condition, which is not directly related to the problem description. This kind of condition is called constraint. The set of possible solutions which satisfy all these constraints is called feasible set.