The technical term for informal, conversational speech is a colloquial speech.
Colloquial, conversational, informal refer to sorts of speech or to usages not on a formal level.
Colloquial language refers to the linguistic style used for casual communication. It constitutes the most common functional style of speech, the idiom normally utilized in conversation as well as other informal contexts.
This linguistic style is characterized by great usage of interjections and other expressive devices.
