Formerly known as the SAT IIs.  Some schools require that you show success not only on formal tests of critical thinking, but also on actual subject material.  The SAT II tests range from Chinese to Math to History.  The schools which require these usually ask for two tests - math and one other subject. Sometimes colleges specify which tests need to be taken; other times the college will ask the student to choose. The College Board (who writes these tests) claims "they provide a dependable measure of your academic achievement and are a good predictor of future performance," but just about any student will tell you that statement is not accurate. However, some schools may use the SAT subject tests as a "placement test" and allow you to skip into a certain level of language mastery or get credits for classes which you already have proficiency. Below is a list of all the tests offered:

English:
Literature

History and Social Studies:
U.S. History
World History

Mathematics:
Mathematics Level 1
Mathematics Level 2

Science:
Biology E/M
Chemistry
Physics

Languages:
Chinese (with listening)
French
French (with listening)
German
German (with listening)
Spanish
Spanish (with listening)
Modern Hebrew
Italian
Latin
Japanese (with listening)
Korean (with listening)