A term attributed to liquid rocket propellants that are liquid at room temperature, and standard pressure. The advantage of using such propellants is that they do not vaporize readily, making handling and storability easy. The disadvantages are that they tend to be somewhat expensive, hazardous, and not as powerful as cyrogenic propellants in terms of specific impulse.
The most powerful storable propellant is UDMH/Nitrogen Tetroxide, which has a specific impulse of around 320 seconds in a vacuum.