What is the relationship between regular expressions and context-free grammars?

Regular expressions and context-free grammars are both formal languages used in computer science to describe patterns in strings. Regular expressions are simpler and more limited in their expressive power, while context-free grammars are more complex and can describe a wider range of patterns. Regular expressions can be converted into context-free grammars, but not all context-free grammars can be represented by regular expressions.