Latent heat
At room temperature the molecules of a solid vibrate. Heating makes them vibrate more and the temperature rises — until the energy is enough to break the bonds between the molecules and let them move freely: the solid melts.
While the state is changing, the heat supplied goes into breaking those bonds, so the temperature does not rise. Once the change is complete, further heat raises the temperature again.
Latent heat
The heat taken in during a change of state, without any rise in temperature, is latent heat.
Latent heat of fusion
Ice at 0 °C taking in heat and becoming water at 0 °C. A solid turning to liquid is melting (fusion).
Freezing water gives the same heat out again.
Latent heat of vaporization
Water at 100 °C taking in heat and becoming steam at 100 °C. The temperature stays at 100 °C until all the water has turned to steam.
Condensing vapour gives the same heat out again.
Figure to be added