An objective function defines the ultimate goal of the model—a mathematical expression to either maximize (e.g., profit, revenue, output) or minimize (e.g., cost, time, waste).

A constraint sets the mandatory limits or conditions within which the goal must be achieved—representing physical, financial, or operational boundaries (e.g., available labor hours, budget limits, minimum production requirements).

In short, the objective function defines what you want to optimize, while constraints define what limits your ability to do so.

An objective function is your main goal—the single target you want to maximize or minimize, such as getting somewhere as fast as possible or earning the highest profit, while a constraint is a strict rule or real-world limit you must follow along the way, such as obeying the speed limit, staying under a $500 budget, or working within an 8-hour shift.