What's an on-ground pool?

[lauriefree]

I have heard this term and wonder if it's a marketing term or if it somehow differs from an above-ground. Is it really any different?

[matt4x4]

All the "on ground" pools I've seen are made out of pieces instead of a continuous wall with one seam. They are supposed to lend themselves better to burrying and are usually available with a hopper style deep end option unlike AG pools.