Plain English Meaning

It is the GPS receiver's built-in ability to check its own work and tell the pilot if the position it is showing is reliable enough to be used for navigation.

Full Definition

The ability of a GPS receiver to independently verify the integrity of the satellite signals it is using for navigation. A RAIM-capable receiver continuously cross-checks signals from multiple satellites and warns the pilot if the position information cannot be trusted to meet the accuracy required for the current phase of flight. RAIM capability is required for a GPS receiver to be approved for IFR navigation, and pilots can perform a pre-flight RAIM prediction to confirm adequate satellite coverage will exist along the planned at the expected time of .