Base
MCAT glossary · Chemical & Physical Foundations of Biological Systems
Definition
A species that accepts a proton (Brønsted–Lowry) or donates an electron pair (Lewis).
Base in plain English
A base is a chemical that likes to grab onto something. In the most common sense (Brønsted–Lowry), a base grabs a proton — a hydrogen with its electron stripped off, basically a bare positive charge — which is the opposite of an acid, which gives protons away. In a broader sense (Lewis), a base is anything that offers up a pair of electrons to form a bond. Either way the theme is the same: bases are the electron-rich "givers/grabbers" that neutralize acids, which is why things like baking soda or ammonia can cancel out something sour or acidic.
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