One of the standout features in Android Lollipop, as demoed at Google I/O, is the ability of each Chrome browser tab to live in the recent apps switcher. In other words, web apps running in the Chrome browser can look and feel a bit more native by appearing in the recent apps.
Right now, this is available in Chrome Beta only, but it should find its way to the regular Chrome app soon enough.
Not everyone likes this feature, though. For people who like to keep tabs on their open tabs (pun not intended!), it can be difficult to manage previous tabs when they intermingle with previously open apps.
Luckily, this feature is easy to opt out of, if you fall into this camp. Simply open up the Chrome browser, navigate to settings, and select Merge tabs and apps. Turn it off, and your tabs will live only in the Chrome browser going forward.