When you browse to a new page in a web browser, the previous page you opened normally dropped from the memory of your computer. There may be cache images and other leftover data, but if you press again, the browser must load most of the page again. The developers of Google Chrome are experimenting with a new "back / front cache" that would cause the previous page to be uploaded instantly.
Simply, when you click on a link on a page, this function will keep the original page frozen in the memory. If you press again, the frozen page is resumed immediately. The Chrome team estimates that this could "improve performance up to 19% of all browsing" in the Android version.
It is interesting to note that Chrome is far from the only browser to experiment with this concept. Firefox used the back / forward cache to some extent from Firefox 1.5 (released in 2005), but it seems to be disabled for HTTPS sites. Safari also had a variation since 2009.
This feature is still in the early stages and there are still security and compatibility issues to solve. At least, it is a great use for the absurd amounts of RAM that many Android flagship now have.