<em>
An acid</em> by definition is a substance that can transfer a proton to another substance while a base is a substance that cab accept a proton.
<em>A proton</em> is a subatomic particle with a positive charge, present in the nucleus of an atom.
<em>An example</em> of an acid base reaction is dissolving sulfuric acid (H2SO4) in water
A proton from sulfuric acid is transferred to water. This proton transfer reaction between the strong acid and weak base, converts water into hydronium ion and sulfuric acid into bisulfate ion.