Sheet music
An orchestral score  or  full score  shows exactly what all the instruments of the orchestra play.  If the piece uses a large orchestra with many different instruments, the page must be very tall.  The conductor uses the score to be able to see which instruments are playing when.  The conductor would cue orchestra members (or sections within the orchestra) when they begin to play.  Conductors do much more than this (tempo, dynamics, interpretation, etc.), of course, but most conductors use a score when rehearsing the orchestra or when the orchestra is performing.