Euphemism

From Wikipedia

A euphemism is a word or phrase that is used in place of a disagreeable or offensive term. When a phrase becomes a euphemism, its literal meaning is often pushed aside. (For instance, in the English language, we have bathrooms with no facilities for bathing, and we rarely use the word gay to describe a cheerful demeanor.) Euphemisms can eventually become taboo words themselves.

Many euphemisms fall into one or more of these categories:

Foreign terms (derriere, copulation)
Abbreviations (F--- you, SOB)
Abstractions (it, the situation, go)
Indirections (behind, unmentionables)
Understatements (visually challenged)
Longer words (perspire, urinate)