Using the LATCH system for car seats
LATCH stands for lower anchors and tethers for children. (In European vehicles it might be referred to as ISOFIX.) Vehicle LATCH systems include hardware referred to as lower anchors (located in the bite of the vehicle's back seats) and top tether anchors. LATCH can make car seat installation easier, by using either the vehicle’s seatbelt OR the lower anchors attachment (but not both).
It is extremely rare to use a top tether with a rear-facing car seat, but all convertible and infant seats have lower anchors for LATCH (some combination seats do as well).
Keep in mind:
There is a weight limit for use of lower anchors of approximately 65 lbs. (which accounts for the combined weight of the child and the car seat). Once a child reaches 40 lbs., it is recommended that the car seat be installed using the seat belt rather than the lower anchors.
Both the LATCH and seatbelt are equally safe when the car seat is installed using the vehicle and car seat owner's manuals. LATCH seems to make installation easier for many parents.
On the car seat you will find a top tether which should be used when installing all forward-facing car seats. Top tethers reduce head excursion in a crash to prevent head, neck and spinal cord injury.
The center rear seat may not allow for LATCH installation. Check the vehicle owner's manual for direction on whether to use seatbelt or lower anchors.