Entry Page Trigger

When you select Entry Page you can specify if you want your change to apply only on the first page of a user's session (Entry Page is True) or on subsequent pages (Entry Page is False).

entry-page

This trigger can be used alone to match on any entry page, regardless of what that page is, or it can be combined with other trigger types. For example, you can combine the Entry Page trigger with a Global Trigger, such as one that matches on blog articles, to show changes only when a user begins their session on a blog article. 
entry-on-blog