Is a pond an ecosystem or community?

It's both. It's both because it depends on what you are including in the pond. An ecosystem includes both biotic (living) and abiotic (non-living) factors. The pond contains both. It contains things like water, rocks, mud, sand, available oxygen, temperature, pH, etc. It also contains living items like bacteria, fish, frogs, etc. That's an ecosystem. A community contains only biotic factors that interact with each other. It's more than likely all of the living things that I listed above influence the quality of the pond itself. That's interaction, and all of those creatures would be the pond's community. If I have to pick between ecosystem and community, I would say that a pond is an ecosystem, because I immediately begin thinking of all of the abiotic factors involved.