Regular languages are a class of formal languages that can be defined using regular expressions or recognized by finite automata. They consist of strings that can be constructed using a finite set of symbols and specific rules. Regular languages are important in computer science, particularly in the fields of compiler design and text processing. These languages can be represented using deterministic finite automata (DFA) or nondeterministic finite automata (NFA), which are theoretical machines that process input strings. Regular languages are closed under operations such as union, intersection, and complementation, making them versatile for various applications in software development and natural language processing.