1. the substitution of a milder, vaguer word or expression for one considered to be offensive or unpleasant.
2. the word or expression so substituted.

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed

A word people use because they like deceiving themselves to believe we live in a Utopia.

Mostly they're used by organizations and "considerate" people who don't want to offend the "situationally disturbed" citizens.

George Carlin, a comedian, did a great schpiel about euphemisms once. (A few of the following examples are in his speech.)

You should read it. It may not "open your eyes," but you'll realize how much we like to disguise our speech and blind ourselves. Disguising a condition with nicer, longer words doesn't change the fact that you still have the condition. Sorry.

(Note: Not all examples {e.g. black/white} are "conditions" or negative at all}

trying to make the mean things you say sound nicer by using different words

The act or an example of substituting a mild, indirect, or vague term for one considered harsh, blunt, or offensive:

Euphemism is an expression intended by the speaker to be less offensive, disturbing, or troubling to the listener than the word or phrase it replaces, or in the case of doublespeak to make it less troublesome for the speaker.

When a phrase is used as a euphemism, it often becomes a metaphor whose literal meaning is dropped. Euphemisms are often used to hide unpleasant or disturbing ideas, even when the literal term for them is not necessarily offensive. This type of euphemism is used in public relations and politics, where it is sometimes disparagingly called doublespeak. There are also superstitious euphemisms, based (consciously or subconsciously) on the idea that words have the power to bring bad fortune (for example, not speaking the word "cancer"; see Etymology and Common examples below) and religious euphemisms, based on the idea that some words are sacred, or that some words are spiritually imperiling (taboo; see Etymology and Religious euphemisms below).

a less direct word used to refer to something unpleasant or embarrassing, often so as to avoid offence.

A word used in place of another to make the listener feel more comfortable, and to make the user more socially acceptable.