Final answer:
The # symbol specifies that the selector is a class.
Step-by-step explanation:
The # symbol specifies that the selector is a class. In CSS, selectors are used to target specific elements on a webpage. The class selector is represented by the # symbol followed by the class name. For example, if you have a CSS rule like .my-class {...}, you can target elements with the class 'my-class' by using the selector #my-class.