A misleading name. There are a fairly large number of purposes for which all-purpose flour is clearly inappropriate. For instance, it makes a pretty awful substitute for sugar in most recipes. And it's not a very good motor oil for that matter. I've heard of no recorded instances where all-purpose flour was used (successfully) as storage media for computer data, either.

To be more accurate, one would want to call this "flour that will work for most purposes where flour is called for" but that's long and awkward. As with many culinary terms, all-purpose flour is named thusly to afford writers of sitcoms with a ready source of gags about cooking-impaired guys and Lucille Ball imitators.

There are a number of specialized flours, such as cake flour, instant-blending flour, pastry flour and self-rising flour that are intended for purposes that are more or less self-evident from their names. The Fannie Farmer Baking Book says that all-purpose flour is "a mixture of various hard- and soft-wheat flours blended to arrive at a medium strength, which has been determined by measuring the protein. This balance of strong and weak flours works very well in baking everything from breads, cookies, and pies to fine, soft cakes." Nothing in there at all about using all-purpose flour as a building material, or as a lubricant, or any number of purposes one might imagine a true literalist might dream up for a flour that styles itself "all-purpose."