GlossaryRetrieval
Long-tail retrieval
Returning relevant results for rare, specific, or obscure queries - not just the popular ones.
Long-tail retrieval is the test that separates serious agent-grade search APIs from toys. Generic search does fine on popular queries ("Python tutorial"). It fails on long-tail queries - a specific code error in an obscure library, a niche academic paper, a less-discussed technical term. Agents in production hit the long tail constantly because that's where users have unsolved problems.