Khums (Arabic: خمس‎ Arabic pronunciation: [xums]) is the Arabic word for One Fifth (1/5). According to Shia Islamic legal terminology, it means "one-fifth of certain items which a person acquires as wealth, and which must be paid as an Islamic tax".

Khums is paid on all items regarded as ghanima, or "spoils of war" and is referred to in the Quran in the sura Al-Anfal ("Spoils"). There is disagreement within Islam about what constitutes ghanima, and thus how far-reaching khums should be. (see below). In the Shia tradition, ghanima is defined as all the profit, or net income in a solar year. In the Sunni tradition for khums, "ghanima" is defined as the spoils of war.

While the concept of Zakat, an obligatory giving of alms, is observed throughout Islam, and is one of the Five Pillars of the faith, the nature of the tax varies considerably between various Islamic traditions. In Sunni tradition, Khums involves a one-fifth payment of only spoils of war. Sunnis pay Zakat, which involves a one-fortieth taxation of total wealth ( and is more akin to a property tax).