What is test form?

A test form is the specific set of questions given at one LSAT administration.

No two forms are exactly equal in difficulty, so LSAC equates each one: every administration gets its own raw-to-scaled conversion table, so a 165 means the same thing no matter which form you took.

That is why a raw-to-scaled table memorized from one practice test does not transfer to another test.

Use the conversion table that came with the practice test you took, and treat other tables as rough estimates.