What is a "kiss"?

Professors of different subjects define the same word in different ways:

Prof. of Computer Science:
A kiss is a few bits of love compiled into a byte.

Prof. of Algebra:
A kiss is two divided by nothing.

Prof. of Geometry:
A kiss is the shortest distance between two straight lines.

Prof. of Physics:
A kiss is the contraction of mouth due to the expansion of the heart.

Prof. of Chemistry:
A kiss is the reaction of the interaction between two hearts.

Prof. of Zoology:
A kiss is the interchange of unisexual salivary bacteria.

Prof. of Physiology:
A kiss is the juxtaposition of two orbicular ors muscles in the state of contraction.

Prof. of Dentistry:
A kiss is infectious and antiseptic.

Prof. of Accountancy:
A kiss is a credit because it is profitable when returned.

Prof. of Economics:
A kiss is that thing for which the demand is higher than the supply.

Prof. of Statistics:
A kiss is an event whose probability depends on the vital statistics of 36-24-36.

Prof. of Philosophy:
A kiss is the persecution for the child, ecstasy for the youth and homage for the old.

Prof. of English:
A 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.

Prof. of Engineering:
Uh, What? I'm not familiar with that term.