Boiling Point
The boiling point is the temperature at which a liquid boils: vapor pressure equals the surrounding pressure. 100 degrees Celsius for water at sea level.
Definition
The boiling point is the temperature at which a liquid's vapor pressure equals the pressure of the atmosphere above it, letting bubbles of vapor form all through the liquid rather than only at its surface, and because it depends on pressure the normal boiling point is defined specifically at $1\text{ atm}$. It is an intensive physical property useful for identifying a substance, since liquids with stronger intermolecular attractions have higher boiling points, and it can be found from the Clausius-Clapeyron equation using a liquid's enthalpy of vaporization; Trouton's rule notes that $\Delta S_{vap} = \Delta H_{vap}/T_b$ is roughly $85\text{ J/mol}\cdot\text{K}$ for many liquids, with hydrogen-bonded liquids like water ($109\text{ J/mol}\cdot\text{K}$) as a notable exception, and dissolved nonvolatile solutes raise the boiling point according to $\Delta T_b = iK_b m$.
Example
Water boils at $100^\circ\text{C}$, rubbing alcohol at about $82^\circ\text{C}$, and cooking oil does not boil until well above $200^\circ\text{C}$; once water reaches its boiling point it stops getting hotter no matter how high the flame, since extra heat just produces more steam, and at the summit of Mount Everest, where pressure is about a third of sea level, water boils near $70^\circ\text{C}$, too cool to brew good tea. Among the group $16$ hydrides, hydrogen bonding makes water the outlier: $H_2S$ boils at $-60^\circ\text{C}$, $H_2Se$ at $-41^\circ\text{C}$, and $H_2Te$ at $-2^\circ\text{C}$, rising with molar mass as expected, yet the lightest of them, $H_2O$, boils at $100^\circ\text{C}$ instead of the roughly $-80^\circ\text{C}$ it would without hydrogen bonding.
Key Insight
Adding salt to pasta water raises its boiling point only by about half a degree for a typical amount, so the real reason to add it is flavor, not faster cooking. Fractional distillation separates liquids by boiling point, and the closer two boiling points are the more theoretical plates a column needs, a principle underlying petroleum refining, liquor production, and even separating liquid air into nitrogen ($-196^\circ\text{C}$) and oxygen ($-183^\circ\text{C}$).