Kiss, in different ways

Here's how the professors of different subjects define the same word, *kiss*, in different ways:
 
* Prof. of Algebra:
A kiss is infinity because two divided by nothing.

* Prof. of Geometry:
A kiss is the shortest distance between two lips.

* 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 salivary bacteria.

* 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 always higher than the supply.
 
* 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 Computer Science:
What is a kiss? It looks to be an undefined variable.