Regular expressions (regex or regexp) are a sequence of characters that define a search pattern. These patterns can be used to match, search, and manipulate text. They are commonly used in text editors, programming languages, and command-line utilities to find and replace text, validate input, and perform other text processing tasks. Regex patterns are made up of a combination of characters and special symbols. These symbols include metacharacters, which have special meanings, and literal characters, which match themselves. For example, the metacharacter „.“ matches any single character, while the literal character „a“ matches the letter „a“. Regex patterns can be used to match specific characters, words, or phrases, as well as to match patterns of characters, such as email addresses or phone numbers. They can also be used to perform more complex tasks, such as splitting text into parts or removing specific characters from a string. In addition, many programming languages include support for regular expressions, allowing you to use regex patterns in your code.