A "reversible seat" refers to a seat that can be facing and positioned in different directions. It can be turned around to face either forward or backward, giving you the flexibility to choose how the seat is oriented. Full definition
In many strollers with reversible seat you need to reverse the seat back before folding. (momsstrollerreviews.com)
Just like with most reversible seat strollers, to reverse the seat all you need is push a button on both sides, swing it around and click it back in. (momsstrollerreviews.com)
Some models have fully reversible seat units so your baby can face you or face away. (jane-uk.com)