DDG kinda nailed it there with her last post. It’s a bit of a fuzzy area, and while I agree it has something to do with the jocks-to-artsies ratio in a given school, it also has to do with the nomenclature used by the staff at said school.
When I was first in Junior High, in 1977, I auditioned for chorus. Ditto for the school musicals. Same in H.S. Try-outs were for jocks of either gender, auditions and rehearsals were for dramatic types of all genders. 
One does not rehearse a double-blind-end-run-triple-bypass-fudge-ripple-delight play for Saturday’s Homecoming game, just as one does not practice Waiting For Godot. ( One could practice patience, but not Waiting…heh ).
The practice v.s. rehearsal thing seems more clear-cut to me, but the try-outs v.s. audition thing seems to be more of a fuzzy area. As I said, the tone was set by the adults running the drama programs at my school.
I sang out of tune but with enormous gusto. 
Cartooniverse
Upon Preview, I might add the following thought. Is it possible that one practices a set piece without altering it on the “field”, whereas one rehearses in a more organic setting where interpretation and alterations occur very frequently? How many defensive backs get to re-write plays for the coach? ( not trying to pick on football teams, honest. ) I’d wager none. How many actors have input into how a scene is read or played? Not none. Not all, but some do and the give and take is frequently the most rewarding part of acting, even at the Junior High or High School level. Perhaps the wording addresses the degree to which a situation can be adjusted/altered/finessed by both child ( actor ) and adult ( coach/director ) ??