Previews are a set of public performances of a theatrical

Theatre

Theatre is a collaborative form of fine art that uses live performers to present the experience of a real or imagined event before a live audience in a specific place. The performers may communicate this experience to the audience through combinations of gesture, speech, song, music or dance...

 presentation that precede its official opening. The purpose of previews is to allow the director and crew

Crew

A crew is a body or a class of people who work at a common activity, generally in a structured or hierarchical organization. A location in which a crew works is called a crewyard or a workyard...

 to identify problems and opportunities for improvement that weren't found during rehearsal

Rehearsal

For other uses, see Rehearsal or Dress rehearsal A rehearsal is a preparatory event in music and theatre that is performed before the official public performance, as a form of practice, and to ensure that all details of the performance are adequately prepared and coordinated for professional...

s and to make adjustments before critic

Critic

A critic is anyone who expresses a value judgement. Informally, criticism is a common aspect of all human expression and need not necessarily imply skilled or accurate expressions of judgement. Critical judgements, good or bad, may be positive , negative , or balanced...

s are invited to attend. The duration of the preview period varies, and ticket prices may be reduced.

The term can also be used to describe an exhibition of a film to evaluate an audience's reaction and make possible changes before its official release. (This is different from a "trailer", a short advertisement for a finished film.) To avoid this confusion, "test screening

Test screening

A test screening is a preview screening of a movie or television show before its general release in order to gauge audience reaction. Preview audiences are selected from a cross-section of the population, and are usually asked to complete a questionnaire or provide feedback in some form. Harold...

" would be a more appropriate term than "preview".