A duck pond is simply a small body of water that is primarily known for being a home to ducks. Often these are artificially constructed as a landscape feature, and in most cases those ponds referred specifically to as a duck pond will, at a minimum, be accessible to humans and fairly pleasing to look at. They often have intentionally peaceful and rustic landscaping surrounding them, and will probably have a footpath along at least one shore. They are popular on university campuses and large estates.
In an interesting cultural wrinkle, it is no longer required for a duck pond to have any relationship to ducks. The term "duck pond" is simply the nicest phrase for a small, decorative body of water. Of course, all the best duck ponds do have some form of waterfowl living in them, but it is by no means required.
In some cases a duck pond will be part of a farm which raises ducks for meat or eggs, or be intended specifically for duck hunting. In this case utilitarian features may be more apparent than aesthetic ones, depending on the tastes of the owners.
Duck pond is also a maritime expression used to refer to a calm spot of water, especially one caused by an oil slick, and most particularly when it was produced intentionally. This can be done to provide a smooth area for seaplanes to land (this practice is not in common use today, because it is hard to clean the floats afterwards), to provide a smooth spot for smaller boats in rough seas, or to provide a calm spot when anchoring in open waters.
Duck ponds might also be formed without oil slicks; pilots of large tankers might turn their ships parallel to the wind to form a large duck pond on their leeward side, protecting their escort ships from the brunt of a storm.
Additionally, duck pond is the common name for a type of portable spill containment berm. it is essentially a tarpaulin designed to be set up like a low, open-topped box. Which is to say, it looks like a small, raised, rectangular swimming pool. These are useful to place under leaks, or to place leaking object into; e.g., under a leaking pipe, or to set a leaking barrel into.
These come in a large range of sizes, usually from 2 to 8 feet on a side, and come with a wide range of supports, from free-standing sidewalls to foam block walls. They are commonly used to place under leaking engine blocks, to set leaking batteries into, or simply to set un compressors or generators that might leak and stain the floor.