A roving, says Wikipedia, is “a long and narrow bundle of fibre [...] usually used to spin woollen yarn.”
I'm sure y'all fibre-arts people knew that already, but I hadn't heard it before.
Wikipedia also says that a roving (I can't even type that without wanting to add “a-roving, for roving's been my ru-i-in”) can be used in thrummed knitting; another term I hadn't heard (in this context) before. The linked-to site says that a thrum is “a little wisp of unspun fleece or roving that is knit into your project every so often,” and adds that “Thrumming makes the insides soft and fuzzy, and freakishly warm.”
Yeah, thrumming does that to me, too. —never mind.