What is Primary?

Legal Definition
That which is first or principal; as primary evidence, or that evidence which is to be admitted in the first instance, as distinguished from secondary evidence, which is allowed only when primary evidence cannot be had.

2. A primary obligation is one which is the principal object of the contract; for example, the primary obligation of the seller is to deliver the thing sold, and to transfer the title to it. It is distinguished from the accessory or secondary obligation to pay damages for not doing so. 1 Bouv. Inst. n. 702.
-- Bouviers Law Dictionary
Legal Definition
First; principal; chief; leading.
See also
-- Black's Law Dictionary