A subspace containment field was a containment field designed to restrict subspace anomalies, like a spatial rupture from expanding.

When a spatial rupture was forming in cargo bay 4 aboard the USS Enterprise-D, caused by solanogen-based lifeforms who were trying to establish a gateway between their tertiary subspace manifold and the regular universe, Geordi La Forge and his engineering team tried to establish a subspace containment field in the cargo bay to stop the anomaly from growing.

They were only able to halt the growth for a short time, however and the containment field failed in the end. Instead, the rupture was bombarded with a coherent graviton beam which closed the rift. (TNG: "Schisms")