A euphemsm is a word or expression used instead of one which may be considered too direct or offensive. The euphemism may intend to amuse or to express politeness. Many euphemisms are a regular part of daily conversation.
Many people use the euphemism pass away rather than die. Another example is ladies' room, which is less direct than ladies' toilet. Fertilizer is less direct than manure.
The term enhanced interrogation is far less direct and expressive than torture. Instead of euthanize, the term put to sleep is often used. The term family planning often replaces contraception.
A euphemism refers to the practice of substituting an unpleasant or harsh word with one which is inoffensive and indirect. This is common in formal situations and in polite company. Many people use euphemisms for sensitive subjects and for decreasing negativity. They're an important part of language.