A sticky footer is a footer that sticks to the bottom of the browser window regardless of the length of the page’s content. If the footer isn’t sticky, it will appear too high on short pages, which doesn’t look good. The best instructions I’ve found for creating a sticky footer for WordPress are found in the WordImpressed.com post Put a CSS Sticky Footer in Your WordPress Theme.
The author explains,
If you’re here, you probably have a footer that likes to ride up to the bottom of your content container. The solution we will implement places the footer wrapper outside of a main wrap that holds all your general content. From there, we will use the power of cascading style sheets to force the footer to stay put at the bottom of the page using some creative and effective styles.
The post shows how to edit your header.php, footer.php, and CSS stylesheet. The post contains helpful code snippets and screenshots. The instructions work for the Twenty Ten and Twenty Eleven themes, and probably many more as well.