Production rules are a set of formal instructions used in computer science and artificial intelligence to define how to transform input data into output. They typically follow the format "if condition, then action," allowing systems to make decisions based on specific criteria. This approach is commonly used in expert systems and rule-based programming. In the context of grammar, production rules describe how sentences can be formed from smaller components, such as words and phrases. Each rule specifies how to replace a non-terminal symbol with a combination of terminal symbols and other non-terminals, helping to generate structured language constructs.