The SAT Subject Tests, often referred to as SAT 2, were a series of standardized tests that assessed students' knowledge in specific subjects. They were separate from the main SAT (now just called the SAT) and focused on deeper content in individual areas like Math IIC, Biology, Chemistry, Physics, History, Literature, etc.
Importantly, the SAT Subject Tests were discontinued in 2021. They are no longer offered and colleges no longer require or recommend them for admission. So, while the term "SAT 2" might still be used, it refers to a testing system that no longer exists.