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A ticket is a voucher that indicates that one has paid for admission to an event or establishment such as a theatre, movie theater, amusement park, zoo, museum, stadium, concert, or other attraction, or permission to travel on a vehicle such as an airliner, train, bus, or boat, typically because one has paid the fare. Also a ticket may be free, and serve as a proof of reservation.
One can buy a ticket at a ticket window or counter, called a box office in the entertainment industry (this term is also used for the total receipts). The ticket check may also be there, or it may be separate. Tickets are also available from resellers. Resellers typically are commercial enterprises that purchase tickets in bulk, and resell them to members of the public, adding a surcharge. Consumers patronize resellers for reasons of convenience and availability. The convenience factor relates to being able to obtain tickets locally, and also being able to make alternate selections on the spot if the preferred performance is not available. The availability factor relates to the fact that all tickets may have been sold out at the box office, requiring the purchaser to either obtain tickets from the reseller, or not to see the show (or at least not see the particular performance of choice).
A ticket may be valid for any seat ("free seating") or for a specific one ("allocated seating"). Sometimes, ex: for some train journeys, both are available, with an increased charge for a reserved seat. Free seating in a train means the risk that one has to stand, but in ex: a cinema it means a seat is guaranteed, just not a specific one.
Paper or card is generally used, although plastic may be used instead for durability. Some have a barcode or magnetic stripe for keeping simple data stored on them, higher end ones use chips to store more data and prevent counterfeiting.
A paper ticket often is perforated so it can be separated into two parts, one (the ticket stub) to be kept by the customer, and one to be kept by the ticket controller. Whether or not one can leave and reenter with the customer part only varies. It may not be allowed to avoid subsequent use of one ticket by multiple people, or even simultaneous use by giving the ticket to someone before the ticket check (if this is physically possible), but it may also be allowed, ex: in a movie theatre to buy, during a movie, a snack or drink before the ticket check and reenter.
Tickets may be printed in advance, or fully or partly printed when issued, or it may be a printed form that is completed in handwriting (ex: by a train conductor who does not carry a ticket machine, but just a supply of forms and a pen).
Security issues 
The fraudulent practice of passing-back a ticket can be overcome by making the ticket in the form of a tamper-proof wristband.
When paying online for admission one may get a code, or a ticket that can be printed out. At the premises, it is made sure that the same right of admission is not used twice.
Internet ticket fraud has become widespread, with authentic-looking but fake ticket websites taking customers' money but not delivering the tickets, notably for the Beijing Olympic Games (through websites not based in China).
Virtual queueing 
Free tickets are applied in virtual queueing. In a place where one has to wait one's turn, there may be the system that one takes a ticket with a number from a dispenser. This system is usually found in hospitals and surgeries, and at offices where many people visit, like town halls, social security offices, labor exchanges, or post offices.
Another form of virtual queuing is where the ticket carries a time-slot on it, rather than just a sequentially incremented number. This type of ticket would allow someone to do other things and then return for a roller-coaster ride, for example, without having to actually stand and wait in line.
Coach ticket 
A coach ticket is a document created by a coach operator or a travel agent to confirm that an individual has purchased a seat on a coach. This document is then used to obtain travel on the operators coach fleet. Only with this ticket is the passenger allowed to board the coach.
A paper ticket is only good for the coach operator for which it was purchased. Usually the paper ticket is for a specific journey. It is sometimes possible to purchase an 'open' ticket which allows travel on any coach between the destinations listed on the ticket. The cost for doing this is greater than a ticket for a specific journey.
Some tickets are refundable. However the lower cost tickets are usually not refundable and may carry many additional restrictions. It is now common for a traveller to print out tickets online and use these on coaches instead of having tickets sent to them in the traditional way. Many coach operators use this system to save costs; some allow a text from the operator to act as a ticket with a unique reference number. Bus tickets are similar.
A pass is a special ticket, representing some subscription, in particular for unlimited use of a service or collection of services. Sometimes the pass replaces the tickets, sometimes it entitles the holder to free tickets. In the latter case, typically both the pass and the ticket has to be shown at the ticket check.
Alternatively, there is the discount pass, for services such as those above: for a fee per unit time (or as a benefit on other grounds) one gets a discount on each purchase. Alternatively, a multi-use ticket (either valid a limited time, or indefinitely) may provide a discount. For example, a pass for entering a cinema 6 times within a year may cost the price of 4 or 5 tickets. A multi-use ticket may or may not be personal. If not, there may be a limitation to the number of people who can use the same multi-use ticket at the same time.
A pass allowing free passage on the SS Christopher Columbus steamship, ca. 1896
See also 
- How to Get Free Movie Tickets - a wikiHow article on getting free tickets to movies.