Sorry friends, but this term has no meaning in digital photography. When you apply a “filter” in photoshop, instagram, or any other app that uses that “concept”, it is rewriting the raster image, throwing out data in the process. But that distinction tells us nothing about the image and only about the photographers workflow and it’s not telling us much. I can generate images in RAW, ie: no filter, that have extreme, “Photoshop-like” characteristics. I can also use all kind of “filters” to no seeming effect.
#nofilter is a high horse that implies a purer photographic image. The main point though is, what that nofilter image looks like is meaninglessly arbitrary. The camera takes the raw data and runs it through the same set of settings you would manually adjust in RAW, except the settings it uses are middle of the road, generally applicable to all situations. If you know how to color correct in RAW you can see what a misguided attempt at correct color the default presets are and also why #nofilter rings hollow.
#nofilter doesn’t mean a pure workflow, it only means you’re trusting a generic preset over your own perception or aspirations. Ironically, shooting with a filter on a film camera would be closer to the spirit of #nofilter than letting a preset determine what your picture looks like in a captured jpg with quite literally no filter on the camera.