I've seen phrases like "Physician-in-ordinary to the Queen". "Oculist-in-ordinary to the Queen", what does mean? https://en.wikipedia.org/wiki/Physician_to_the_Queen
This is covered by a different Wikipedia article:
In relation particularly to the staff of the British Royal Household, and more generally to those employed by the Crown, ["in ordinary"] is used as a suffix showing that the appointment is to the regular staff, for example a priest or chaplain-in-ordinary, or a physician-in-ordinary, being a cleric or doctor in regular attendance.
In other words, this physician is just a regular employee of the monarch. The title's (literally) baroque wording is a result of the jumble of traditions and protocols surrounding the British monarchy. It's not something that would be used anywhere else, for example the ship's doctor on a cruise ship is unlikely to have "in ordinary" in his or her title.