Low Head Track is used when you dont have enough ceiling height for track with a normal radius. If you notice on the picture this track has two tracks-one for the top section and one for the other 3 bottom sections. This allows you to have a sectional garage door with low ceiling height instead of a one peice door.
There are two different types of low head track- low head-0" and low head-3".
Whoever comes out to estimate your door will know which you might need.