The definition of a base as a compound that accepts a proton was first described by Johannes Nicolaus Brønsted and Thomas Martin Lowry independently in 1923.

This is known as the Brønsted-Lowry theory of acids and bases.

Here's a breakdown:

* Brønsted-Lowry acid: A substance that donates a proton (H+).

* Brønsted-Lowry base: A substance that accepts a proton (H+).

This theory expanded upon the earlier Arrhenius theory of acids and bases, which defined acids as substances that produce hydrogen ions (H+) in solution, and bases as substances that produce hydroxide ions (OH-) in solution.