Definition of Kiss

Economics:
Kiss is that thing for which the demand is always higher than the supply.

Accountancy:
Kiss is a credit because it is profitable when returned.

Algebra:
Kiss is infinity because two divided by nothing.

Geometry:
Kiss is the shortest distance between two lips.

Physics:
Kiss is the contraction of mouth due to the expansion of the heart.

Chemistry:
Kiss is the reaction of the interaction between two hearts.

Zoology:
Kiss is the interchange of salivary bacteria.

Physiology:
Kiss is the juxtaposition of two orbicularisoris muscles in the state of contraction.

Dentistry:
Kiss is infectious and antiseptic.

Philosophy:
Kiss is the persecution for the child, ecstasy for the youth and homage for the old.

English:
Kiss is a noun that is used as a conjunction, it is more common than proper, it is spoken in the plural and it is applicable to all.

Architecture:
Kiss is a process which builds a solid bond between the two dynamic objects

Computer Science:
What is a kiss? It seems to be an undefined variable.