Evaporation
Evaporation is vaporization that occurs only at the surface of a liquid, at any temperature below the boiling point, as the fastest particles escape.
Definition
Evaporation is the change from liquid to gas that happens only at the surface of a liquid, at any temperature below the boiling point, when the fastest-moving particles there gain enough energy to escape into the air; because the most energetic particles leave first, the average energy of what remains drops, which is why evaporation cools a liquid down. This is driven by the high-energy tail of the Maxwell-Boltzmann speed distribution, where molecules whose kinetic energy exceeds the intermolecular binding energy break free of the surface, and in a closed container that escape is eventually balanced by condensation, establishing an equilibrium vapor pressure that depends only on temperature and the strength of the liquid's intermolecular forces; in open air the net evaporation rate depends on the difference between that vapor pressure and the vapor's partial pressure in the surrounding gas.
Example
A puddle dries up after rain stops and wet clothes dry on a line in the breeze as their water evaporates into the air, and rubbing alcohol feels cold on skin precisely because it evaporates fast and carries heat away with it. A shallow dish of water dries faster than the same amount in a tall glass simply because more surface area is exposed. At $25^\circ\text{C}$ the vapor pressure of water is $3.17\text{ kPa}$, of ethanol $7.9\text{ kPa}$, and of diethyl ether $71\text{ kPa}$, so ether evaporates fastest of the three because its weak dispersion forces let molecules escape most easily, and at $100\%$ relative humidity net evaporation stops entirely because the vapor's partial pressure already equals its vapor pressure.
Key Insight
Evaporation is what makes you feel chilly stepping out of a warm pool, and evaporative cooling is exactly how sweat regulates body temperature, how a wet-bulb thermometer measures humidity, and why humid heat feels worse than dry heat, since the energy removed is the full enthalpy of vaporization, about $2400\text{ J}$ per gram at skin temperature. Boiling and evaporation are both vaporization, but boiling happens throughout a liquid at one specific temperature while evaporation happens only at the surface across a whole range of temperatures.