Brønsted-Lowry Concept

Acids
With the Brønsted-Lowry concept we usually refer to a hydrogen ion as a proton. That is because a proton is all that is left when a hydrogen atom loses an electron to become an ion.
Brønsted and Lowry independently came up with the idea that an acid is an acid because it provides or donates a proton to something else. When an acid reacts, the proton is transferred from one chemical to another. As will be noted later, the chemical which accepts the proton is a base.

Bases
Note that in order for an acid to act like an acid, there needs to be something for it to react with. There needs to be something to take the proton. There needs to be a base. A base is a proton acceptor. Compare this to the definition that an acid is a proton donor.
Bases are the opposite of acids. Bases are basic because they take or accept protons. Hydroxide ion, for example can accept a proton to form water. Brønsted and Lowry realized that not all bases had to have a hydroxide ion. As long as something can accept a proton it is a base.