MOCA

MOCA. See minimum obstruction clearance altitude.
Mode C. Altitude reporting transponder mode.
MRA. See minimum reception altitude.

MOCA-
(See MINIMUM OBSTRUCTION CLEARANCE ALTITUDE.)
MODE- The letter or number assigned to a specific pulse spacing of radio signals transmitted or received by ground interrogator or airborne transponder components of the Air Traffic Control Radar ...

MOCA--Minimum obstruction clearance altitude is the lowest altitude in between radio fixes that meets clearance requirements but only gives navaid reception within 22 miles of the navaid.

Minimum obstruction clearance altitude (MOCA)
Minimum reception altitude (MRA)
Minimum safe altitude (MSA) ...

Often seen near a shower in moist areas and affects the ceiling limits. Results in sudden visibility reduction in mountainous terrain making flight below MOCA (Minimum Obstacle Clearance Altitude) impossible without ground violations.

allows sign-off of annuals IMC Instrument Meteorological Conditions - flying in conditions below those required for VFR flight; colloquially, "in the clouds" IMHO in my humble opinion LTA Lighter Than Air MEA Minimum Enroute Altitude (IFR) MOCA ...

See also: ILS, Direct, Report, Obstacle, Air traffic