Alms are material goods or monies that are given to the needy as a corporal work of mercy. An obligation to give alms arises out of natural law and divine precept. It is a serious obligation of charity and not of justice, and hence the goods or monies are to be given out of one's surplus. It is not required that one gives unless: his obligation to his family are first satisfied, his needs for personal comfort and social position are met, or the money is not otherwise owed in debt. Services of professional persons are considered alms when offered free of charge. However, alms are not be confused with other works of charity such as fraternal correction or acts of a spiritual nature.

Source; Catholic Encyclopedia, Thomas Nelson Publishing, 1996