Failures to extract result in a fired cartridge case stuck in the chamber. Unless it was the last cartridge in the magazine, another unfired cartridge gets stripped by the slide and jammed against the head of the fired case in the chamber.
This particular malfunction has rightly or wrongly often been categorized as a "double feed" malfunction. I agree that for this particular scenario the term "failure to extract" is probably more precise. But a failure to extract does not always result in an unfired cartridge jammed against a fired case, for example if the failure to extract occurred with the last round in the magazine.
But that is not the only type of double feed malfunction. A bad magazine can cause a double feed resulting in an unfired cartridge in the chamber, and another unfired cartridge is jammed against its head. This occurs when the magazine lips allow a cartridge to pop out of the magazine when the slide hits the rearward extent of its travel and then strips off a second cartridge behind the first. This type of double feed is undoubtedly less common than the failure to extract, but it does occur.
Both types of "double feed" malfunctions are dealt with in the same manner and it is not immediately obvious to the shooter whether the cartridge in the chamber if fired or unfired. Here is a short article and very short video describing how to deal with a double feed malfunction:
http://www.nrablog.com/articles/2016/7/nra-firearm-training-tip-double-feed-stoppage/
When shooting, it is not always obvious what type of malfunction has occurred. Note that in the video the shooter first tries to clear the malfunction with a quick tap-rack which does not work. The shooter then locks the slide to the rear which eases some of the pressure on the magazine, strips the magazine, clears the pistol of the fired or unfired cartridge by racking the slide three times, reinserts the magazine (or preferably a different loaded magazine), racks the slide to chamber a round, and shoots.
The article says that the slide must be locked back before stripping the magazine. Not all agree with this. For example, this is a good video on how to deal with malfunctions of all types by Clint Smith who does not recommend locking the slide back first:
http://www.youtube.com/watch?v=BfyULpEhmug