A pond is an area of water that has fish, plants and living creatures in, it is a habitat for them. where as a pool is clean water, where you would go to swim with no living beings in it.
To make it more complicated, there is a new interest in "natural filtration" swimming pools. They are strategically made ponds that use plants and algae for filters. Most are concrete or fiberglass and have mechanical pumps. They are like koi ponds for people, kinda cool I guess.