The Back Stance (dwi kubi seogi) is performed with the leading foot pointed directly forward, the rear foot perpendicular at a 90 degree angle from the front foot. (This is why it it sometimes called an L Stance, your two feet are placed like the letter L. See also, Left Stance and Right Stance.)
The front foot is about one stride (three foot lengths) in front of the rear foot, so that the heel of the front foot points back directly to the heel of the rear foot. Most of the weight (about two thirds) should be on the rear leg. Both legs are bent at the knees, and both feet are flat on the floor.
Naming the Back Stance Edit
In most schools, the term right back stance means that the right foot is back. In other words, the left foot is forward. Conversely a left back stance means the left foot is back, the right foot is forward.
This can be confusing for some students, since for most other stances the "right" version of the stance means that the right foot is forward. For example in a right front stance the right foot would be forward.