Acrylic partials were developed as provisional restorations. Technically these are "Mucosal-borne provisional prostheses." They are also used when the remaining teeth are likely to be removed in the near future and the partial needs to be easily added on to so that the partial denture can become a full one.
"Acrylic partials" without clasps were often called "Stayplates." These are not technical, or prothodontic terms but rather convention or sloppy terms that stick in the verbage. I was always taught that "Flipper" was a porpoise and not a dental device, but docs and patients call them that out of common usage perhaps because they "flip around" in the mouth.
Older patients called complete dentures and removable partial dentures, "full plates" and "partial plates" respectively. Some patients refer to a removable partial denture as a "removable bridge."
This is also the case in "Fixed Prosthodontics." The actual term for a fixed (cemented, luted, "glued") restoration replacing missing teeth is a "Fixed Partial Denture." We all tend to refer to these as "Bridges" even though this is not the actual, "correct" term.
These are all terms of various, and perhaps less-correct usage. People spend portions of their careers defining "Glossary of Prothdontic Terms," and arguing accuracy of semantics. Simply look up the history of the term "centric relation," and how many times it has been redefined over the years!!!
Sorry for the rant and even more verbose explanation... just sayin'.