Tutti is an Italian word literally meaning all or together and is used as a musical term, for the whole orchestra as opposed to the soloist. It is applied similarly to choral music, where the whole section or choir is called to sing.
2) An orchestrator may specify that a section leader (e.g., the principal violinist) plays alone, while the rest of the section is silent for the duration of the solo passage, by writing solo in the music at the point where it begins and tutti at the point he wishes the rest of the section to resume playing.
3) In organ music, it indicates that the full organ should be used: all stops and all couplers. (This organ usage is sometimes instead indicated as fff.) To simplify this changing over, many organ consoles offer a toe stud or a piston to call the tutti: Pressing once begins the tutti, and pressing again reverts to the previous registration.
In Italian, tutti is plural, tutto is the singular form.