Consonants involve constrictions, or gestures that narrow the vocal tract at a particular point.
Most consonants use only one constriction, but some have more than one. In order to fully describe a consonant sound, we need to describe each constriction as well as some other properties of the vocal tract. These should be specified for every constriction involved in a consonant. Answering each of these questions about the state of the vocal tract is enough to uniquely identify any consonant. If two consonants are different, they must differ in their answers for at least one of these questions.