What does adhesion mean?
The definition of adhesion
Ad*he”sion, n.
Etym: [L. adhaesio, fr. adhaerere: cf. F. adhésion.]

1 The action of sticking; the state of being attached; intimate union; as the adhesion of glue, or of parts united by growth, cement, or the like.
2 Adherence; steady or firm attachment; fidelity; as, to error, to a policy. His adhesion to the Tories was bounded by his approbation of their foreign policy. De Quincey.
3 Agreement to adhere; concurrence; assent. To that treaty Spain and England gave in their adhesion. Macaulay.
4 (Physics)
The molecular attraction exerted between bodies in contact. See Cohesion.
5 (Med.)
Union of surface, normally separate, by the formation of new tissue resulting from an inflammatory process.
6 (Bot.)
The union of parts which are separate in other plants, or in younger states of the same plant.

— Adherence; union. See Adherence.