Is there any difference between virtual and stack raster(in QGIS). Observed features are more contrast in virtual rather stack raster. Also, while classification does it makes any difference to use one over the another
A raster stack has several rasters above one another, they overlap and have (more or less) the same extent: see here for an image. A stack is used e.g. if you have imagese for the same area, but at different times.
A virtual raster however is a kind of tiles, one next ot each other, thus each one having different extent. As a virtual raster, they all get stiched together to form one large, connected raster - like a mosaic.