What does "adherence" mean?

Adherence: The state of being fixed in attachment; fidelity; steady attachment; adhesion; as, adherence to a party or to opinions. These words, which were once freely interchanged, are now almost entirely separated. Adherence is no longer used to denote physical union, but is applied, to mental states or habits; as, a strict adherence to one's duty; close adherence to the argument, etc. Adhesion is now confined chiefly to the physical sense, except in the phrase "To give in one's adhesion to a cause or a party."