I've read about cryogenic storable liquid rocket engine but since it doesn't refer to its fuel, I want to understand the difference between a cryogenic and a cryo-storable engine. The term cryo-storable is found in the document Multidisciplinary design optimisation of Expendable Launch vehicles
Based on page 31 of the document referenced in the question, the author appears to use the term for engines that use one cryo propellant and one storable one (for example, liquid oxygen and kerosene). It's not a term I have heard before.
Prop: integer variable defining the type of propellants used for new design rocket engines. The following alternatives are considered:
o Prop=1: liquid cryogenic engine, burning Liquid Hydrogen (LH 2 ) and Liquid Oxygen (LOx).
o Prop=2: liquid cryo-storable engine, burning Rocket Propellant One (RP1) and LOx.
o Prop=3: liquid storable engine, burning Mono-Metil Hydrazine (MMH) and Nitrogen Tetroxide (N 2 O 4 ).
o Prop=4: solid propellant engine with a fixed Ammonium Perclorate (AP), Hydroxyl-Terminated Poli Butadiene (HTPB) and Aluminium powder formulation.
Cryogenic: the propellant has to be cooled to keep it in a liquid state. At room temperature, it's a gas. Oxygen, hydrogen for example. These propellants need careful handling because they are at very low temperatures.
Storable: the propellant is a liquid at room temperature, so the rocket can sit on the launch pad with propellants on board without needing to vent boiloff or refrigeration. Examples: RP-1, MMH, UDMH.
This is desirable, because it makes launch delays easier to handle. The drawback of most storable propellants is that they're toxic, so they need careful handling. Some of these propellants are hypergolic, i.e. they burn when they come in contact with each other.
Cryo-storable would then be a rocket that uses one cryogenic and one storable propellant (e.g. oxygen and RP-1).