||This article needs additional citations for verification. (July 2012)|
A rehearsal is an event that occurs as preparation for a performance. It is undertaken as a form of practising, to ensure that all details of the subsequent performance are adequately prepared and coordinated. Most commonly employed in the performing arts as preparation for a public presentation, rehearsals are nevertheless used in other contexts, as well, to prepare for the performance of any anticipated activity.
Dress rehearsal 
For theatre, the dress rehearsal is a full-scale rehearsal where performers work out every detail of the performance. Cast members wear their costumes, and the backdrop may be used with props. For a musical performance, the dress rehearsal is the final rehearsal before the performance.
In a theatre or opera house 
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-throughs. 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 and stage movement.
A Q-2-Q or cue to cue is a type of technical rehearsal and is intended primarily for the lighting and sound 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—when lights have to be turned on, sound effects triggered, and items rolled on and off the stage—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 tops 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 (who pay a reduced ticket price), 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. Audience members typically pay a lower price to attend a preview performance.
In traditional Japanese Noh theatre, performers primarily rehearse separately, only rehearsing together once, a few days before the show. This is to emphasise transience of the show, in the philosophy of "ichi-go ichi-e", "one chance, one meeting".
Professional ensembles 
A professional orchestra or chamber ensemble rehearses a piece in order to coordinate the rhythmic ensemble and ensure that the pitches of the different sections match. A professional ensemble will typically only rehearse an orchestral work for two or three rehearsals which are held several days before the first performance. A professional ensemble is less likely than an amateur orchestra to play the entire piece. Instead, a professional ensemble will typically review passages which pose challenges for the ensemble from the point of view of rhythmic or harmonic coordination. An example of a passage that might pose rhythmic coordination challenges would be a contemporary work which involved polyrhythms, in which one section of the orchestra plays a rhythm in 4/4 while another section plays a melody written in 5/4. An example of harmonic challenges would be a work in which the orchestra has to perform dissonant, complex harmonies. The conductor calls out bar numbers or rehearsal letters to direct the orchestra to different sections which he or she would like to perform.
For works that present a particular challenge for certain sections (e.g., a complex, exposed passage for the viola section), orchestras may have section rehearsals or sectionals in which a section of the orchestra (e.g., the woodwind players or the double basses) rehearse on their own under the direction of the Principal player in the section, or, in some cases, also with the conductor (e.g., in the case of a very rhythmically-challenging piece).
Prior to rehearsing a concerto with an orchestra, a soloist will 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 to sound out the tempo prior to the commencement of a piece. 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. In some orchestras, there may be a limited audience during the dress rehearsal (typically university music students).
Amateur ensembles 
Amateur orchestras or chamber ensembles, such as university or community groups rehearse music for a number of reasons. While an amateur ensemble does rehearsals to coordinate the rhythmic ensemble, rehearsals are also held for a number of other reasons. In amateur groups, rehearsals are used by the leader to teach ensemble members about the different playing styles and tones used in music from different eras. As well, orchestra conductors select pieces so that players can learn new skills, such as more complicated rhythms. For an amateur ensemble, the rehearsals are often used to give the players an opportunity to have repeated chances to play difficult passages. Amateur groups are much more likely than professional groups to hold sectional rehearsals. Another difference between rehearsals in an amateur orchestra and a professional orchestra is the number of rehearsals. A community orchestra or university ensemble may have ten or even fifteen rehearsals over several months to prepare a major symphony; a professional orchestra might prepare that same symphony in two rehearsals over two days.
In an amateur performance consisting of miscellaneous items it is common to have 'a walk through rehearsal' on the concert day where actors walk through their moves on and off stage without actually performing their items.
In other contexts 
|Look up rehearsal in Wiktionary, the free dictionary.|
The use of rehearsals and dress rehearsals extends beyond the performing arts. When an organization has to learn how to implement a new process, it may rehearse the activity beforehand. Emergency-planning organizations often rehearse their preparations for responding to civil disasters. Armies that are planning an attack on a certain target may create a mock-up of the target and rehearse the attack. The introduction of major changes to complex industrial and technical fields, such as information systems is often rehearsed, particularly where this requires multiple activities to be coordinated and completed within time constraints. Many companies undertook major initiatives to rehearse the changes associated with the Year 2000 problem and the economic and monetary union of the European Union.
See also 
- "Dress rehearsal". Merriam Webster. Retrieved 2012-15-07.