Distance
From FreeSpace Wiki
Distance (Status operator) Returns the distance between two objects. These can be ships, wings, or waypoints. When a wing or team is given (for either argument), the result will be the closest distance. NOTE: The standard retail SEXP measures between the center of one ship and the bounding box of another. It is recommended to use center-distance or bbox-distance. Returns a numeric value. Takes 2 arguments... 1: The name of one of the objects. 2: The name of the other object.
Comments
Commonly used to determine if a ship is close enough to a node to warp out, but it should also be widely used in the departure cue of ships that are supposed to jump at the end of a waypoint path. Using are-waypoints-done-delay may not work because ships oftentimes miss the waypoint and turn around it in a futile attempt to catch it. Using a distance check would not only prevent this, but would also give a more realistic warpout effect because the ship will not slow down to 0 before departing.
In FreeSpace Open, this SEXP is no longer displayed in FRED, as it has been replaced with distance-to-center and distance-to-bbox. However, missions with the classic distance SEXP will continue to work as before.