1.
casual speech; informal language; peer language
Informal speech used between equals or close friends, as opposed to polite or honorific language. Characterized by plain verb forms and casual vocabulary. Often discussed in the context of Japanese social hierarchy and age relationships.
Etymology
タメ comes from the gambling term meaning "same" (same score/rank), referring to people of equal standing. 口/口 means "speech" or "way of talking."
Cultural note
In Japanese society, the choice between 敬語 (polite language) and タメ口 is an important social decision. Using タメ口 with someone older or of higher status is generally considered rude, while switching from 敬語 to タメ口 between peers signals growing closeness.