Definition
CROSS (FIX) AT OR BELOW (ALTITUDE)
Used by ATC when a maximum crossing altitude at a specific fix is required. It does not prohibit the aircraft from crossing the fix at a lower altitude; however, it must be at or above the minimum IFR altitude.
- See: MINIMUM IFR ALTITUDES
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).