Define latent heat of water?

is the amount of heat that must be supplied to1 kg of water (at constant pressure and temperature) to obtain1 kg of saturated steam.

The energy released or absorbed during any phase change process by a body is called the Latent Heat. For example the melting of ice is a phase change process from solid to liquid and boiling of water is a phase change process from liquid to vapor, the heat energy associated with these two processes is termed as Latent Heat. 

Latent heat is the energy released or absorbed by a body(water) during a constant-temperature process. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of water. Phase transistion temperature is different at different pressure (I.e boiling temperature of water is different at different pressure)