When curtains open from the middle to the right and left of the track, it is called Center Open (or Split Draw / Center Draw). Center Open is the most common type of draw.
When a curtain is pulled open to only one side of the track, it is a one-way draw curtain track. The most common reason to use a one-way draw curtain track is that there's an obstacle in the way on the other side. The obstacle may be a chair, sofa, or even a wall.