Line of Dance: An imaginary line (compass of sorts) used to indicate the direction of traffic and how to move on the dance floor.

In ballroom, you are often dancing with other couples. So, how do we dance to minimize the number of collisions? In addition to Floorcraft, one of the basic techniques is simply Line of Dance (LoD).

Normally, a ballroom is usually in the shape of either a rectangle or a square. So imagine a rectangular room. Now imagine a rectangle smaller than said room. Looking down from the ceiling, couples move in a counter-clockwise direction traveling along this rectangle. Hence, LoD is determined by where you are. Note that LoD does not apply to all dances. Spot dances for example, such as cha-cha, rumba, and jive don’t have LoD. But Progressive dances, such as waltz and tango, do have LoD so that couples move in the same general direction and do not crash into each other. For a general characterization, all standard dances (tango, waltz, Viennese waltz, quickstep, and foxtrot) are progressive dances and of the latin dances, only samba and paso doble are progressive dances.

Now back to your perspective on the floor. Line of dance is relative to yourself, depending on where you are on the rectangle. But the direction that you would move in to travel along a wall (counterclockwise looking from above the floor) is known as facing line of dance. From that, there are seven other directions that can be derived. Here are all 8 directions, each direction being 45 degrees counterclockwise to the previous direction:

Facing Line of Dance: Directly facing LOD.
Diagonal to Center
Center
Backing Diagonally to Wall
Backing Line of Dance
Backing Diagonally to Center
Wall
Diagonal to Wall

Note: Center is the Center of the Room. Wall is the Wall you are traveling along LoD.

In addition, when turning corners, your LoD will rotate 90 degrees counter-clockwise. So what was originally direction Center will then become your new LoD when you travel along a new wall.

And there you go! That's line of dance!