From AMS Glossary
(Also called geodynamic meter.) The standard unit of dynamic height, defined as 10 m2 s−2; it is related to the geopotential ϕ, the geometric height z in meters, and the geopotential height Z in geopotential meters by
where g is the acceleration of gravity in meters per second squared. (Some sources prefer to give the constants 10 and 9.8 with units of meters per second squared so that the units of ϕ and Z would be the same as those of the geometric height.)
The dynamic meter is about 2% longer than the geometric meter and the geopotential meter.