SAT Reasoning Test: This is the standard SAT test that includes three sections: Reading, Writing and Language, and Math. Most schools require all applicants to take this test.
SAT Subject Tests: These are optional tests that you can take in addition to the SAT Reasoning Test. Each Subject Test focuses on a specific subject, such as Math Level 1, Math Level 2, Physics, Chemistry, Biology, U.S. History, World History, and Literature. Some schools may require or recommend certain Subject Tests for admission to specific programs or majors.
If you are unsure of which schools you will apply to, it's generally recommended to register for the SAT Reasoning Test and at least one SAT Subject Test in a subject area that you excel in. This will give you the flexibility to apply to a wider range of schools.
You can find information about the SAT requirements for specific schools on their admissions websites. It's a good idea to research the requirements of your target schools well in advance of the SAT registration deadline to ensure that you have enough time to prepare and register for the appropriate tests.