Plain English Meaning
OROCA is a number printed on en route charts that tells you the lowest altitude in that area where you would clear all known terrain and obstacles by a safe margin. It is a backup reference, not a cleared altitude to fly.
Full Definition
An off-route altitude shown on IFR en route charts that provides obstruction clearance with a 1,000-foot buffer in non-mountainous areas and a 2,000-foot buffer in designated mountainous areas. OROCA is computed for an entire quadrangle on the chart and does not guarantee navigation signal coverage, communications coverage, or compliance with ATC routing or . It is as a reference for or off- situations, not as an altitude.