Hi, Christine:
A zero entry pool has one end that starts at zero depth (like at the water's edge at the beach) and gets deeper as you go into the pool. It is a benefit if you have nonswimmers, as they can sit/play in shallow depth water, or if you have a handicap that would limit your ability to climb down steps or require the use of a water chair (sort of like a pool wheelchair). Families with children like a zero entry pool as little ones can safely play/be monitored at the zero depth end while older kids can be at the deeper end with the slides, etc. Many of the deluxe resorts have at least one zero entry pool (GF, Poly, AKL, YC/BC....not sure about others). HTH