What does adherence mean?
The definition of adherence
Ad*her”ence, n.
Etym: [Cf. F. adhérence, LL. adhaerentia.]

1 The quality or state of adhering.
2 The state of being fixed in attachment; fidelity; steady attachment; adhesion; as, adherence to a party or to opinions.

— Adherence, Adhesion. 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.”