Cadillac 2007 STS Owner's Manual page 45

A forward-facing child seat (C-E) provides restraint
for the child's body with the harness and also
sometimes with surfaces such as T-shaped
or shelf-like shields.
A booster seat (F-G) is a child restraint designed
to improve the fit of the vehicle's safety belt
system. Some booster seats have a shoulder belt
positioner, and some high-back booster seats
have a five-point harness. A booster seat can also
help a child to see out the window.
45