what is kiss?

Here is how the professors of different subjects define the same word-kiss-in different way.
Kiss is indifinity because two divided by nothing.
Kiss is the shortest distance between two lips.
Kiss is the contraction of mouth due to the expansion of the heart.
Kiss is the reaction of the interaction between two hearts.
Kiss is the interchange of salivary bacteria.
Kiss is just the position of two orbicularis muscles in the state of contraction.
Kiss is infectious and antiseptic.
Kiss is a credit because it is profitable when returned.
Kiss is that thing for which the demand is always higher than the supply.
Kiss is an event whose probability depends on the vital statistics of 36-24-36.
Kiss is the persecution for the child,ecstacy for the youth homage for the old.
Kiss is a noun that is used as a conjuction,it is common than proper,it is spoken in the plural and it is applicable to all.
What is kiss? It looks to be an undefined variable.
Kiss is a process which builds a solid bond between the two dynamic objects.
Kiss is illegal in some circumstance.