Defensive patent aggregation

Defensive patent aggregation (DPA) is the practice of purchasing patents or patent rights to keep such patents out of the hands of entities that would assert them against operating companies. The opposite is offensive patent aggregation (OPA) which is the purchasing of patents in order to assert them against companies that would use the inventions protected by such patents (operating companies) and to grant licenses to these operating companies in return for licensing fees or royalties.

Source: Wikipedia — Defensive patent aggregation (CC BY-SA 4.0)