Phase change refers to any transformation or transition that occurs between different states of matter, such as from solid to liquid, liquid to gas, etc.
Boiling point is the temperature at which a substance changes from its liquid state to its gaseous state under standard atmospheric pressure.
Melting point is the temperature at which a solid substance changes from its solid state to its liquid state under standard atmospheric pressure.
Sublimation is when a solid directly transforms into its gaseous state without first becoming a liquid.