Here's a blurb they provided:
This reference card puts the power of jQuery selectors at your very fingertips. Written by Bear Bibeault and Yehuda Katz, co-authors of jQuery in Action (Manning Publications), jQuery selectors are one of the most important aspects of the jQuery library. These selectors use familiar CSS syntax to allow page authors to quickly and easily identify any set of page elements to operate upon with the jQuery library methods. Understanding jQuery selectors is the key to using the jQuery library most effectively.