Pages Visited targeting allows you to create campaigns that target visitors who have seen a specific number of pages/URLs in the same session.
This is a hugely powerful target and allows you to build campaigns that align with a journey you often see customers taking on site. For example, you might be aware that a lot of low intent traffic comes to your site via your blog - using Pages Visited targeting allows you to surface discount messaging at a prominent point in their journey to improve their conversion rate.
Users can only be targeted during their current session using this target. This is to keep campaigns relevant to your site users' current browsing behaviour.
You can use Pages Visited Targeting to identify users who have come from PPC, email or another medium that uses query parameters within the URL. If you don't have this setup, you can use Google's Analytics URL Builder to help you create universally identifiable URLs.