Garmin 55 AVD Owner's Manual page 63

Velocity/time terms:
GS Ground speed. GS is the speed measured relative to the ground;
also known as velocity over ground (VOG).
VMG Velocity made good. VMG is velocity in the direction of the desired
course. It is the speed at which you are closing on the "active to"
waypoint.
ETE Estimated time enroute. ETE is the time it will take to reach the
"active to" waypoint based on VMG.
Direction terms:
DTK Desired track. DTK is the course between the "from" and "to"
waypoints.
BRG Bearing. BRG is the direction from your position to the "active to"
waypoint.
CTS Course to steer. CTS is the recommended direction to steer in order
to reduce cross track error and stay on course (see Section B.2 for
an example using CTS).
CMG Course made good. CMG is the bearing from the "active from"
waypoint to your position.
TRK Track. TRK is the direction of movement relative to the ground.
TRN Turn instruction. TRN is the difference between BRG or CTS
(whichever you have displayed) and TRK. "L" indicates you should
turn to the left, "R" indicate you should turn to the right. The degrees
indicate the angle you are off course.
Distance terms:
RNG Range. RNG is the great circle distance from your position to the "to"
waypoint.
DMG Distance made good. DMG is the distance from the "active from"
waypoint to your position.
STR Steer direction and distance. "L" indicates you should steer to the
left, "R" indicates you should steer to the right. The distance
indicates how far you are off course.
B-2