An acid can be determined using a pH scale. When the substance or element scores seven or less on the pH scale, then it is considered to be an acid. When the substance or element scores more than seven on the pH scale, then it is considered to be a base. An acid by definition is one in which it can donate a proton.
A base is the opposite of the acid. It is the substance that can take a proton and not donate it. An acid base neutralization is one in which both the acid and base on a reaction do react equally. Both acids and bases in the equation are equal on both sides of the chemical equation.