Cross linking refers to allowing users to navigate to web pages within your website via cross reference. This could also be done within pages of partner websites. Cross links can help users get access to helpful information while navigating web pages.
Websites make use of cross linking mainly for providing complimentary product selection, up-selling/cross selling products etc. There are websites which provides tutorial links that navigates to a different section on the website that educates the user how to play around in the webpage, or using their products or services, later would provide links to get back to the previous page where they initially where. The idea is to keep tutorials/help components separate from the commercial aspect of the website, but still make it available to the users via links.
Cross linking websites if not done properly can cause harm to your overall SEO campaign. There are certain cross linking methods that could be considered as black at seo techniques by Google.
For e.g. , if your web pages provide tight link rings without any outside websites linking in, this might get your website penalized by Google.
Google also checks for the contents provided within cross linked website; if Duplicate contents are identified within such pages this would adversely affect your rankings.
Cross linking is a great way to enhance user experience. However doing so should not be done purely for the search engines alone.