Regular expressions, commonly known as regex, are a powerful tool in Python for pattern matching within strings. They enable developers to perform complex text processing tasks such as searching, validating, and manipulating data efficiently. By utilizing the built-in re library, users can access various functions like re.search() to find specific patterns, re.findall() to retrieve all matches, and re.sub() to replace patterns within strings. Regex is particularly useful in natural language processing, data cleaning, and validation tasks, making it an essential skill for programmers and data scientists alike.