"Pj" as it appears in pet registry data is almost certainly a paperwork artifact — the initials P.J. entered into a name field without periods, then normalized to title case as "Pj." The actual pet was probably registered under a fuller name or uses the two-letter spoken form P.J., which reads entirely differently from a single word.
What P.J. Actually Is
As a spoken pet name, P.J. works fine. Initials names have a long domestic tradition — casual, affectionate, and slightly retro. "P.J." could stand for anything or nothing at all; many pets acquire them simply because the owner's kid gave them a name starting with those letters. The Labrador Retriever community seems to have a particular fondness for initial-based names, probably because Lab owners tend to name with family-friendly approachability in mind.
Owner-Type Signal
Initials names on pets usually signal owners who either inherited the name from a child in the household or who enjoy names that feel personal without requiring explanation. "What does P.J. stand for?" is a natural conversation opener, which has its own social utility at the dog park.
Registry Note
If you arrived here looking for a name spelled exactly "Pj," that spelling will create practical friction — most people will read it as a typo or mispronounce it. The intended form is almost certainly P.J. Browse all pet names for similar short, snappy options.