Regular expressions, often abbreviated as regex, are sequences of characters that form a search pattern. They are commonly used in programming and text processing to find, match, or manipulate strings of text. By defining specific patterns, users can efficiently search for complex text structures, such as email addresses or phone numbers, within larger bodies of text. These patterns can include various elements like literals, character classes, and quantifiers, allowing for flexible and powerful text matching. Regular expressions are supported in many programming languages, including Python, Java, and JavaScript, making them a versatile tool for developers and data analysts alike.