Definitely a cutout as already advised. Very commonly found for many some Victoria and New South Wales issues. Some are from postcards so are on thicker card stock. As far as collectable, nope, only the complete item is, a cutout is considered a damaged form. Plenty of these types are commonly seen as false "Imperf varieties" of the regular stamp to pass them off as expensive rarities or even proofs by scammers. So be careful when buying. I think they are worth keeping in my collection labelled as Cutout. Its part of the postal history and when its related to an area I particularly collect. The same sort of cutouts can be found for various Australian issues. USA and Great Britain too and no doubt many others.