Most fish species in the world live in water temperatures between the mid-60�F and 90�F. However, most species that one may find in aquariums tolerate temperatures between 75�F and 82�F.
When an aquarist mentions cold water s/he usually refers to the types of fish that do not require their water to be heated at any time. The water temperature for goldfish for instance, is quite varied and could range from 32�F to 80�F+.
Cold water as a definition has many grey areas. The White Cloud minnow does not need heated water, but their tolerance is considerably less; between 60�F and 75�F will keep them happy.