Patentleft

Patentleft is the practice of licensing patents (especially biological patents) for royalty-free use, on the condition that adopters license related improvements they develop under the same terms. Copyleft-style licensors seek "continuous growth of a universally accessible technology commons" from which they, and others, will benefit.

Patentleft is analogous to copyleft, a license that allows distribution of a copyrighted work and derived works, but only under the same or equivalent terms.