Does the phrase ".78/280/250" have a standard meaning to an airline pilot, in the context of a long descent?
It means the profile is based on descending at 0.78 Mach until the IAS increases to 280 knots, at which point that speed is maintained to 10,000', at which point the aircraft slows to 250 knots for the remainder of the descent until it's time to slow &amp; configure for landing. That 0.78/280/250 is a very standard profile for descent planning in the 737, although variations such as 0.80/320/250 or 0.76/250 are certainly possible.