Skiing/Skating – Skiing and Skating are closely linked in Legions. Skiing was the old technique used in Tribes to reach incredible speeds, which involves reducing the friction between a player and the ground. Velocity was accumulated through jumping on the downslope and jumping in conjunction with jetting on the upslope. Legions follows a similar premise, though skating is introduced. Skating creates a cushion of air between the player and the ground resulting in zero friction, and allows a player to maintain speed across flatter areas. Skiing is still needed to achieve high speeds, though use of up-jetting on inclines and conservative down-jetting on declines.*
*Not to sure about this, could munge give a better explanation?
"Skating" (energy skating) in Legions is done by activating the energy cushion below the player (a spring force away from the ground surface) that allows them to glide. Skating can mean either coasting along the ground in that state or using your energy coils to push yourself across the ground while your energy cushion is active. When your energy suit is active, the boots automatically fire on when you're close enough to the ground. That means that from a player's perspective, skating is moving along the ground while your energy suit is activated (RMB by default).
"Skiing", as it's used in Legions, describes the act of using the energy cushion system along with the directional thrust of the energy coils (forward, back, left, right, up, or down) to skillfully take advantage of the slopes in the terrain and ramps on structures to fluidly move through the world while gaining speed. This involves converting your momentum in one direction to momentum in another direction using objects in the world. Downward momentum from falling or jetting can be efficiently converted into lateral momentum by landing on a steep slope that banks in the direction you wish to go. Lateral momentum can then be converted back into vertical momentum by using energy to launch off of an upward slope. Skiing also involves a bit of energy management and timing.
"Ski" normally implies speed and grace. A player could be in the air or on the ground while they are skiing. "Skate" is just a description of the mode of movement and has no implication as to speed. A skating player could be going extremely fast or extremely slow, but they are most definitely coasting along the ground.
A rabbit is anyone who just skis/skates/jets around as fast as they can, normally with no particular route in mind, though it's normally used in Legions to describe people in CTF who grab the flag and then take off around the map to avoid being killed in the hopes that their flag will be returned and they will be able to capture. It's generally a bad tactic in public games (at least on smaller maps) because unless your team is organized you're not likely to be able to get back to your base to cap before someone from the enemy team can make a speed grab. That's why it leads to frustrating stalemates and a rabbit is generally seen as coward and/or a bad sport.
Grabber, capper, and runner (for "flag runner", like "rum runner") are synonymous - someone who grabs the enemy flag (from the enemy base or via a planned pass from another capper) and tries to bring it home for a capture. Runner does not imply rabbiting or running away, it only means you're trying to "run" the flag from the enemy base to yours.
It's a tactical position, not a behavior (e.g. defender, chaser, escort, runner, etc). For example, someone who was escorting their flag runner back to their base and then picked up and subsequently captured the enemy flag after an unfortunate drop is still not a flag runner, though they're probably a good escort (assuming they weren't the one to kill the runner).
The correct term for the person who is currently holding the flag is "flag carrier" and it has no implications as to position. For example, a defender could at some point become the flag carrier (via pass or drop), but unless they leave their post at the base they are still playing defense.