(Latin: placeo, please)
Etymologically it means delight or gratification.
According to Saint Thomas it results from the perfection of activity, for whenever activity is perfectly exercised, pleasure is present, and is proportionately augmented as the activity becomes more perfect.
Morally considered, pleasure is the satisfaction obtained from the possession of good.
Hence, pleasure may vary according to the appetite considered.
It is spiritual, if it resides in the will; it is sense pleasure, if it resides in the sense organs.
Spiritual pleasure is morally good or bad according as the object is good or bad.
Sense pleasure has its morality from the usefulness to moral good or at least its compatibility with moral good as seen by the agent.
Pleasure indulged in with due regard for law is not sinful.
New Catholic Dictionary