A rehearsal is a preparatory event in music and theatre (and in other contexts) that is performed before the official public performance, as a form of practice, and to ensure that all details of the performance are adequate for professional presentation.
In theatre, a performing arts ensemble rehearses a work in preparation for performance before an audience.
Rehearsals that occur early in the production process are sometimes referred to as run-through's. Typically a run-through does not contain many of the technical aspects of a performance, and is primarily used to assist performers in learning dialogue and to solidify aspects of blocking.
A Q-2-Q or cue to cue is a type of technical rehearsal and is intended primarily for the technicians involved in a performance, although they are of great value to the entire ensemble. It is intended to allow the technicians and stage manager to rehearse the technical aspects of a performance and identify and resolve glitches. Performers do not typically rehearse entire scenes during Q-2-Q's, but instead only perform dialogue or actions that are used by the stage manager as a marker for when to initiate technical sequences or cues (hence the title). Abbreviated Q-2-Q's in which only the opening and closing sequences of each act or scene are performed is sometimes referred to as top's and tails. It is rare for any but the most technically complex performances to have Q-2-Q rehearsals outside of technical week.
Cue to cues are often preceded by a dry tech, in which the technicians rehearse their cues without the actual performers present at the rehearsal.
A dress rehearsal is a rehearsal or series of rehearsals in which the ensemble dresses as they will dress at the performance for the audience. The entire performance will be run from beginning to end, exactly as the real performances will be, including pauses for intermissions. An open dress is a dress rehearsal to which specific individuals have been invited to attend as audience members. They may include patrons, family and friends of the ensemble, or reviewers from the media. The dress rehearsal is often the last set of rehearsals before the concert performance and falls at the end of technical week.
A preview, although technically a performance as there is a full audience; including individuals who have paid for admission, is arguably also a rehearsal in as far as it is not uncommon in complex performances for the production to stop, or even return to an earlier point in the performance if there are unavoidable or unresolvable problems.
Rehearsing a musical composition often involves repeating some passages over and over again until everyone in the ensemble masters them. Rehearsal letters can be very helpful for this purpose.
Orchestras often have section rehearsals or sectionals in which a section of the orchestra (e.g., the woodwind players) rehearse on their own.
Prior to rehearsing a concerto with an orchestra, a soloist will often rehearse it with a pianist substituting for the entire orchestra (thus, two pianists in the case of piano concerti).
To help with tempo in solo or chamber rehearsals, a metronome may be used.
For music performances, a dress rehearsal does not imply dressing in performance concert dress. It is merely a final rehearsal before performance where generally the ensemble will run through the entire program as if there is an audience.