If a recipe calls for a vegetable oil, it generally means an unflavoured or very mild-flavoured oil such as Crisco, Canola, Corn Oil or Sunflower Seed Oil.
You might think that all edible oils are vegetable oils, but they're not: there are nut oils, and there are fish oils -- whale oil, for instance, was popular not so long ago. You could sort of class olive oil as a vegetable oil, but generally it's considered to be in a class by itself, and, if anything, olives are technically "fruit."
Some vegetable oils are blends from sources such as corn, rape or sunflower seed, or soybeans. Others may be all from one source.
Manufactures aim for a high-smoke point and a neutral taste to make the oil as all-purpose as possible.
In 1957, the Wesson Oil company put pressure on Clementine Paddleford, America's foremost food writer at the time, to use the phrase "vegetable oil." Competing phrases were "all-purpose oil" and "liquid shortening." There is the possibility that they also threatened to pull their advertising from This Week magazine if Paddleford didn't comply. She did, after a trip down to New Orleans where they wined and dined her. 
Literature & Lore
 Alexander, Kelly and Cynthia Harris. "Hometown Appetites." New York: Gotham Books. 2008. Page 192.
Vegetable OilsCorn Oil; Soya Oil; Vegetable Oils
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Huile végétale (French); Aceite vegetal (Spanish); Kadalennai (Indian)