I learned a new German word today, Waidmann, but I already knew the word Jägermeister, so I wondered what the difference between them is. When would a German use one over the other?
In the end both mean the same.
The usage of "Jägermeister" is obsolete. Nowadays when saying "Jägermeister" you usually refer to the alcoholic drink.
"Weidmann" or "Waidmann" is the technical term used by hunter and is also well known in "Weidmannsheil" and "Weidmannsdank", a greeting.
The informal term is just "Jäger"
They both mean the same thing, a hunter. According to Wikipedia, a Jägermeister was quite literally a master hunter.
Note, though, that today, under pretty much all circumstances, "Jägermeister" will be confused with the liqueur of the same name, and "Waidmann/Weidmann" is an outdated term that may not be understood at all except for the "Waidmanns Heil" ("good luck") expression.
Occupational titles change with the society that bestows them.
Jägermeister is an obsolete occupational title for a professional* hunter after a three year apprenticeship and an examination for a master craftsman's certificate (Meisterprüfung). It was current from around 1600 until the early 20th century. Today it is the name of a popular digestif (Kräuterlikör).
Waidmann – originally referring to anyone catching any kind of animal, later having the two more specific meanings "fisher" and "hunter" – is an even older occupational title, which was slowly displaced by "Jäger" from around 1600 onwards. It survives in popular folk songs and poetry when a romantic image of a huntsman is to be evoked, as well as in traditionalist hunter's lore.
Jagdmeister The job titles today are "Revierjäger", "Revierjagdmeister" (after a Meisterprüfung), Revieroberjäger (after 10 years as Jagdmeister) and Wildmeister (after 10 years as Oberjäger). [Source: http://www.revierjaeger.de/ernennungen]
*professional here meaning a job, not the quality
Waidmann/Weidmann has it's origin in the verb "auswaiden" which means taking the guts out of an animal. So a Waidmann is s.o. who hunts animals and can take their guts out and prepare them to be edible. Jäger/Jägersmann (Jägermeister (old)) do pretty much the same but it's shorter so more common and more often used.