Wildcards are symbols that replace one or more letters or characters in a search term. They are helpful when you want to make sure you will find variants of your search term - child - children.
Single character wildcard: ? - Wom?n will find women or woman
Multiple character wildcard: * - environment* will find environment, environments, environmentalist, etc.
You can also place the * in the middle of a word. This is especially helpful for when you are unsure of the spelling. Wol*z will find Wolfowitz.