standard overall average noise figure (of a mixer diode) (OS)

The overall average noise figure when the average noise figure of the IF amplifier is a specified standard value (usually 1.5 dB) and the passband of the IF amplifier is sufficiently narrower than that of the mixer so that the mixer conversion loss and output noise temperature are essentially constant over the IF passband.

References: 

JESD77-B, 2/00
RS-311-A, 11/81