What is the difference between a regular expression and a regular language?

What is the difference between a regular expression and a regular language?

A regular expression is a sequence of characters that defines a search pattern, used for matching strings. It is a compact and concise way to represent a set of strings. On the other hand, a regular language is a set of strings that can be generated by a regular expression or recognized by a deterministic finite automaton (DFA). In other words, a regular expression is a notation to describe a regular language. While a regular expression is a representation of a pattern, a regular language is the actual set of strings that match that pattern.