They're also listed, from left to right, "Skinny" to "Loose": Skinny, Straight, Boot, Authentic, and were listed as such before there was a "Skinny" fit. In practice, I can fit more easily into size 29 Authentics than size 29 Straights. I own a pair of size 29 Straights and size 28 Standards, and while both are listed online as being "straight through the leg," the Straight has a slimmer thigh than the Standards, even at a size larger. Finally, the Authentic is described as the "perfect hybrid" between the Standard and Straight fits. You can also look at the fit pictures -- while I can't confirm that the same fit model is used for all of them, it simply looks like the Straight fit is slimmer. Also, doesn't it seem like the Authentic fit was altered with the new models (the one with the straight line stitching across the back pockets) to be a little more relaxed? I e-mailed Gap about whether the fit has changed since it was first introduced, and they told me: "Although we don't have specifics on any proportion changes, it would not be unusual if they aren't slightly different from their original introduction."