Animated GIFs = GIFs
When anyone says GIF nowadays they are almost always referring to animated GIFs. This linguistic phenomena is commonly known as synecdoche—a figure of speech where a part represents the whole, or vice versa—and has seemed to happen within the last few years.

The GIF file format, of course, can exist as both a still image, and as an animated series of images. Even though GIFs were never “intended as a platform for animation…,” both manifestations of the file format have been serving internet culture quite well for some time.
“The Graphics Interchange Format is not intended as a platform for animation, even though it can be done in a limited way.”
—from the GIF89a Specification, Appendix D
Static image GIFs with captions (usually set in Impact Bold white with a black outline) have become more academically known as image macros, while animated GIFs have become known, simply, as GIFs.

This shorthand can probably be linked to the massive proliferation of animated GIFs between 2011 and 2012. Although I can’t reference any one event when this wide-scale shorthand adoption occurred, I can certainly point to a few milestones in the popularity of animated GIFs where the abbreviated reference might have made talking about the medium much simpler.
[Animated] GIF Milestones 2011–2012
Feb 5, 2011 T. Finn of Something Awful urges members to take a doctored GIF of El Hadji Diouf and visualize what tripped him
Feb 13, 2011 Jamie Beck and Kevin Burg create their first photographic loop with all but a few details masterfully masked in After Effects for repetitive motion. They dub the resulting moving image and technique to create them “Cinemagraphs,” and the term and technique have persisted ever since.

October 14, 2011 Flixel is founded with the intent of bringing Cinemagraph creation to the masses
2012 Presidential election year in the United States; bloggers, journalists, and other media outlets on social media use GIFs to great effect. Some campaigns themselves embrace the trend.

Jan 10, 2012 The largely-visual blogging platform, Tumblr expands its GIF-uploading limit to 1MB from 500kb (already larger than the limits of social networks that accept the format at all — at this time Facebook and Twitter did not); blog-creation on the platform quickly exceeds 50M
Jan 28, 2012 The New York Public Library launches The Stereogranimator, away for users to create so-called “wobble GIFs” or “wiggle GIFs” using the library’s extensive archive of images
April, 2012 – October, 2012 Jason Eppink, associate curator of Digital Media at The Museum of the Moving Image exhibits We Tripped El Hadji Diouf, a collection of animated GIFs responding to T. Finn’s challenge in 2011
July 2, 2012 Elspeth Reeve of The Atlantic Wire writes about the US Gymnastics team, illustrating her comments with GIFs, sourced heavily from the Gymanstics GIFs Tumblr feed
July 3, 2012 The New York Times posts a piece by dance critic Alastair Macaulay supplementing his writing with auto-playing video. Though the file format was not technically a GIF, the looping photographic format is reminiscent of cinemagraphs
July 28, 2012 Brian Floyd of SB Nation summarizes a Michael Phelps reaction to losing a 400 IM race to Ryan Lochte using a GIF
July 30, 2012 Kevin Lincoln of Buzzfeed recaps an Olympics fencing match controversy using GIFs
August, 2012 Andy Yaco-Mink, a developer at Buzzfeed, experiments with Rubbable GIFs and open sources the code to expand (and potentially monetize) the news outlet’s already-extensive use of GIFs
October 3, 2012 The Guardian and Tumblr “live GIF” the US presidential debate
November 12, 2012 Oxford American Dictionaries choose “to GIF” as the word of the year
Read more elsewhere…
GIF verb to create a GIF file of (an image or video sequence, especially relating to an event): he GIFed the highlights…blog.oxforddictionaries.com
The Choosy Folks at Oxford American Dictionaries Choose... GIF 2012 Word of the Year Tuesday, November 13, 2012-Oxford…blog.oxforddictionaries.com
"We have now obtained the doubleeyed or twin pictures, or Stereograph, if we may coin a name. But the pictures are two…stereo.nypl.org
Like all memes, the animated GIF must constantly evolve or die, and from the looks of the recent GIF innovations, we…www.thewire.com
It seems all cute and quirky and fun that President Obama's campaign emailed supporters four GIFs of the president…www.thewire.com
Gymnastics is one of those Olympics sports that lots of people watch every four years, meaning whatever happens during…www.thewire.com
From my fourth-floor inland Brooklyn apartment, I see the Statue of Liberty as I lie in bed without even lifting my…www.nytimes.com
The Michael Phelps vs. Ryan Lochte battle never materialized on Saturday as the latter breezed to an easy win in the…www.sbnation.com
Did you hear about the Olympic fencer who refused to leave the piste after losing to a computer glitch? I didn't watch…www.niemanlab.org
The animated GIF will be further enshrined as a reporting tool during the first presidential debate Wednesday, when…www.poynter.org
What is it about small, repetitive moving images that everyone is so crazy about on Tumblr? Animated GIFs have been…mashable.com
Giudecca May 14, 2006 quote: However due to reasons I can't comment on at this time I am legally prevented from using…forums.somethingawful.com
On February 5, 2011, T. Finn, a member of the comedy website Something Awful, posted a doctored animated GIF of…jasoneppink.com
