The term 'COLORFUL POND FISH' can be summarized as a type of fish known as KOI, which is a three-letter word. KOI are ornamental varieties of domesticated common carp that are kept for decorative purposes in outdoor ponds and water gardens. They are known for their vibrant colors and patterns, which can range from white, black, red, orange, yellow, blue, and cream. KOI are popular among hobbyists and are considered a symbol of luck and prosperity in many cultures.