What is a Kiss???

So, what is a kiss in professors's term?

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

Prof. of Engineering:
Uh, What? Im not familiar with that term.