To clarify, anything etched in vinyl isn’t technically a dubplate. ‘Dubplate’ is the Jamaican term for a one-off acetate disc that is cut on a lathe, in a mastering studio (rather than pressed to vinyl in a plant). In the past (before other portable media like cassettes, CDRs, etc.), acetates were the only means by which you could demo tracks recorded in the studio, at home or elsewhere. Hence the term ‘test cut’ (not to be confused with a ‘test press’, which is the last stop before manufacturing). The cutting of an acetate is also the first step in the process of creating the ‘mother’, and from that, the ‘master’, which is used to stamp grooves into heated vinyl in a pressing plant. In the Jamaican tradition, dubplates took on an extra role as one-off, custom versions of songs that were exclusive to this DJ or that. Your status was in your arsenal of dubplates. Jungle and other dancehall-descended scenes took up the practice. Usage of the term started getting muddied in the mid-00s when dubstep DJs were still cutting them, but people on forums started calling CD-Rs, mp3s, etc. ‘dubs’.
As mentioned above, acetate-coated aluminum discs differ physically from vinyl records. The most common size is ten inches. They otherwise look more or less the same as a vinyl record, but they smell different - imagine burnt crayons. And whereas even a heavyweight vinyl record has some flex to it, a dubplate/acetate is rigid and brittle feeling. Rap it with your knuckle and it almost pings. Dubplates wear out with use, because the acetate is comparatively soft, but how quickly depends on how you treat them. Heavy needles and a lot of back-cueing will wear them out fast, but with care they can last indefinitely. Dubplates have a bit of an aura around them. They’re rare - because they’re hard to acquire and cost a lot ($50-100/disc, depending where you are) - and, as physical media, they’re ephemeral.
Custom-cut vinyl started appearing more and more in the 00s. I think it was Vestax that launched a system that cost only a few thousand dollars, compared to tens of thousands for a Neumann lathe. They weren’t known for their sound quality, but I think that’s supposed to have improved. These one-off records are less expensive to make and don’t wear out the same way a dubplate does. You lose a bit of the aura, and the unusual material qualities of dubplates (which do make them feel like a different medium), but they’re probably more practical.
I wrote more than I meant to, there, but the long and short of it is that people like using the word ‘dubplate’, but there are important distinctions between actual dubplates/acetates and lathe-cut vinyl. So anyone selling “vinyl dubplates” is playing a bit fast and loose with terminology and history.