A rational agent is an agent that has clear preferences, models uncertainty via expected values of variables or functions of variables, and always chooses to perform the action with the optimal expected outcome for itself from among all feasible actions.

A rational agent can be anything that makes decisions, typically a person, firm, machine, or software.

Rational agent can be defined as an agent who makes use of its percept sequence, experience and knowledge to maximize the performance measure of an agent for every probable action. It selects the most feasible action which will lead to the expected results optimally.

For every percept sequence a built-in knowledge base is updated, which is very useful for decision making, because it stores the consequences of performing some particular action.

If the consequences direct to achieve desired goal then we gwt a good performance measure factor, else, if the consequences do not lead to desired goal, then we get a good performance measure factor.

For e.g. if agent hurts his finger while using nail and hammer, then, while using it for the next time agent will be more careful and the probability of not getting hurt will increase. In short agent will be able to use the hammer and nail more efficiently.