The term 'temperate' is normally used to describe species that live between temperature ranges of 16-22C (60-71F), whilst cold water fish live in a cooler range, and tropical fish prefer warmer conditions. Unheated aquariums kept in normal heated room conditions usually settle within the 'temperate' range.
There are several species of aquarium fish, often sold as tropical or cold water species, which can be kept in temperate water. Choosing temperate species should be done with care since some naturally temperate species may have been heavily bred, which causes their tolerance for cooler water to diminish (e.g. Guppies) and commercial varieties may only be suitable for warmer water.