What is a regular expression?

A regular expression is indeed a sequence of characters that defines a search pattern. This powerful tool is widely used in various programming languages and text processing applications to perform tasks such as searching, matching, and manipulating strings. Regular expressions use special syntax that allows for complex search criteria, enabling users to specify patterns that may include characters, digits, whitespace, and other character classes.

For instance, if you are looking to find all occurrences of email addresses in a large text document, you can use a regular expression to specify the pattern that an email address follows (e.g., containing an "@" symbol followed by a domain). This makes it much easier to extract or validate data as compared to manually checking each string for conformity to the desired format.

The other choices provided do not accurately describe a regular expression. Methods for handling errors in scripts, debugging tools, and types of variables pertain to other programming concepts that serve different purposes than defining search patterns.