What is a "regex"?

Regex is an abbreviated term for "regular expressions", and is a standardized set of text that can help you find what you're looking for quickly.  For example, /w typically means to match character from A-Z or 0-9, in upper or lower case, while ^nst typically means to find anything that begins with n, s, or t.

A cheat sheet and more information about regex can be found here.