This document discusses idioms and their relationship to semantics and pragmatics. It defines idioms and categorizes them on a spectrum from transparent to opaque. Various scholars' classifications of idioms are presented based on factors like formality, field of use, and comparisons. Idioms are used to make language more colorful and convey subtle meanings. Examples are provided. Idioms present problems for compositionality since their meanings are not derived from the parts. The relationship between idioms, context, and speakers/hearers is explored, noting how idioms can violate conversational maxims. Cultural differences in idioms across languages are highlighted.