Awkward title, I know. Let’s assume you play an oboe and the oboe is only used a few times during a very long piece of music. Does your copy of the music have page after page of rests until your notes?
Back in high school, when I played the cello, a long rest was indicated by a rest with a number above it. The number was the number of measures that we were supposed to rest.
Usually it’s one whole measure rest with a number over top, indicating how many measures you are supposed to count out until you come in. Then your part. Then another Measures of rest sign.
If you don’t play at all during a movement, the music may simply say (for example): Mvt. II Tacet.
Back when I was in high school, I took a trip with some school music groups. My main role was playing guitar for the jazz ensemble, but the concert band was short of percussionists so I filled in - my only job was to play the triangle.
The sheet music was completely hilarious. Measure rest with 73 at the top, then two measures with a couple triangle hits, measure rest with 45 at the top, then 1 measure with a final triangle hit…
It shoud be noted that most orchestral music for the individual instruments rarely runs past two pages. Remember, all it usually needs is one staff for most of the instruments, and combined with the multiple measures of rest convention, it’s usually pretty easy to put a LOT of music on one page.
ETA: Longer pieces like the longer movements of a concerto will have more pages, as will something like a violin score with a lot of really intricate playing.
As a percussionist, I frequently had music that looked like the triangle part mentioned above. Well, not quite that bad. Usually they would merge parts. Like, I’d play triangle here, wood blocks here, cymbals there, back to triangle, back to cymbals, etc. It was, at times, an athletic event running around the back of the orchestra!
