LATCH goes by a few different names. Canadian readers might be familiar with UAS or CANFIX, and European readers may know of ISOFIX.
In any case, it refers to an international standard for child safety seats and their attachment points in cars. Car manufacturers in the US are required to abide by LATCH. Standard attachment points for child safety seats have been manufactured into cars in the US since September of 2002, allowing all recent car seats to be secured into all recent cars safely and easily.
LATCH stands for Lower Anchor and Tethers for CHildren. Vehicles now come equipped with lower anchors in the seats, and tether options to strap a child safety seat over the car seat itself.
If you drive an older car, you may not have Lower Anchors, although you can still typically utilize Tether Anchors. Cars manufactured in the 90s generally have a pre-drilled hole for a Tether Anchor. Ford, GM, and Chrysler will install one Tether Anchor free of charge in most of their older vehicles.
Even without Tether Anchors or Lower Anchors, Car seats can be installed with only the seat belt. Retrofitted tether anchors, or LATCH anchors, are for added security. If you do not have access to any added security beyond the standard seat belt, it is suggested that you keep your child rear-facing for as long as possible.