Condensation
Condensation is the phase change from gas to liquid that happens when a vapor cools or is compressed enough for its particles to cling together.
Definition
Condensation is the phase change from gas to liquid, the reverse of vaporization, that occurs when gas particles lose enough energy for attractive forces to pull them together, happening when a vapor cools below its dew point or is compressed, and it releases the same amount of heat that vaporization originally absorbed. It occurs whenever the partial pressure of a vapor exceeds its equilibrium vapor pressure at the local temperature, making the liquid phase lower in free energy, and like freezing it requires nucleation, so in the atmosphere condensation nuclei such as aerosols, dust, and salt let droplets form at only modest supersaturation, while perfectly clean air can hold vapor that is significantly supersaturated; the released latent heat is what powers convection in thunderstorms and hurricanes.
Example
Water drops form on the outside of a cold glass of lemonade because invisible water vapor in the air condenses on contact with the cold surface, and a bathroom mirror fogs during a hot shower for the same reason. Clouds form when rising air cools until its water vapor condenses onto dust particles, and air at $30^\circ\text{C}$ and $60\%$ relative humidity holds water vapor at a partial pressure of about $2.5\text{ kPa}$, so cooling it to its dew point near $21^\circ\text{C}$, where water's vapor pressure also equals $2.5\text{ kPa}$, starts condensation; a refrigerator works the same cycle in reverse, condensing compressed refrigerant vapor in its rear coils and dumping the released heat into the kitchen.
Key Insight
Condensation actually warms its surroundings, which is why steam burns are worse than boiling-water burns: condensing steam dumps an extra $2260\text{ J}$ per gram onto skin before it even starts cooling as liquid water. Distillation is nothing more than controlled evaporation followed by condensation to separate liquids by vapor pressure, and a refrigerator, an air conditioner, and a power plant's steam turbine all run on that same vaporization-condensation cycle, moving heat around by moving a substance between phases.