Browsers have become one of the most memory-intensive applications you can run and while vendors such as Google and Firefox have gone to great lengths to keep things under control, for some users, it's still not good enough. In fact, Chrome will introduce a rather drastic measure in an upcoming version — tab "discarding" — to help alleviate the issue.
As Google's François Beaufort explains, when Chrome detects a high amount of memory pressure, it'll take a look at your open tabs, pick one or more that are the least important, and unload their contents. The tab itself will remain open, but its memory usage will be reduced to a fraction of its original consumption.
If this behaviour sounds familiar, it's because Chrome OS has this feature built-in. It's also very similar to how an extension called The Great Suspender works.
The feature isn't currently available in the stable build of Chrome, but it could be integrated with a patch at any time. Once it is added, it'll have its own experimental flag
chrome://flags/#enable-tab-discarding and internal page
A question you probably have is how Chrome decides which tabs are OK to discard. A page on the Chromium website provides some guidelines, though it's hard to say if the precise logic detailed there will be applied to the desktop version.