The use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered more acceptable when used socially.
An expression should be considered "true slang" if it meets at least two of the following criteria:
- It lowers, if temporarily, "the dignity of formal or serious speech or writing"; in other words, it's likely to be considered in those contexts a "glaring misuse of register."
- Its use implies that the user is familiar with whatever is referred to, or with a group of people who are familiar with it and use the term.
- "It's a taboo term in ordinary discourse with people of a higher social status or greater responsibility."
- It replaces "a well-known conventional synonym". This is done primarily to avoid discomfort caused by conventional phrases or by further elaboration.