This document discusses reference, sense, and referring expressions in semantics. It defines semantics as the study of meaning in language. Reference deals with the relationship between language and the world, while sense deals with relationships inside language. There are two types of reference: variable reference, where a word can refer to different things, and constant reference, where a word always refers to the same thing. Sense is the place of an expression in a system of semantic relationships with other expressions. A referring expression is any expression used to refer to something, and can be indefinite or definite depending on the context. Opaque contexts and equative sentences are also discussed in relation to referring expressions.