What is an artesian pool?

Do you mean an artesian well? Artesian is the name brand of a pool & spa company. Here is some information on artesion wells - I would assume the same is true for the poools.

An artesian well allows water to rise to the surface that has traveled through porous rock from a higher elevation. This pumpless well seems to defy gravity because the pressure that builds up between layers of rock gets relieved when the water finds a path to the open air. For nearly a thousand years, people have drilled wells to drink such cold, filtered water that doesn't need to be hauled up from the depths.

An aquifer provides the water source for an artesian well. An aquifer is the layer of permeable rock, like limestone or sandstone, that absorbs water from an inlet path at high elevation such as the top of a mountain. The water source might be fed by snowmelt or precipitation. Porous stone is sandwiched between a top and bottom layer of an impermeable substance like clay soil or shale rock. This keeps the water pressure high, so that when you get to a point below the entryway of the flow, there is enough pressure to bring the water up. Natural springs form in the same way when a gap in the impermeable rock, maybe triggered by an earthquake, allows the water to rise to the surface.

its a make of a pool is all