The term 'informal lexicon' refers to a type of language that is not considered to be part of the standard language. It includes words and phrases that are used in everyday conversation, but are not found in formal dictionaries. SLANG is a type of informal lexicon that is often used by certain groups of people, such as teenagers or members of a particular profession. SLANG words and phrases are typically used to express emotions, ideas, or feelings in a more casual way than standard language.