A prop, formally known as (theatrical) property,  is an object used on stage or screen by actors during a performance or screen production.  In practical terms, a prop is considered to be anything movable or portable on a stage or a set, distinct from the actors, scenery, costumes, and electrical equipment.   
During the Renaissance in Europe, small acting troupes functioned as cooperatives, pooling resources and dividing any income. Many performers provided their own costumes, but other items such as stage weapons or furniture may have been acquired specially and considered "company property".  
Some suggest the term comes from the idea that stage or screen objects "belong" to whoever uses them on stage. 
There is no difference between props used in theatre, film, or television. Properties director Bland Wade said "A coffee cup onstage is a coffee cup on television, is a coffee cup on the big screen." adding "There are definitely different responsibilities and different vocabulary." 
During a performance props are set up in order, off stage on a table in an easily accessed area or pre-set on-stage before the performance begins by the assistant stage manager (ASM). The person in charge of preparing, maintaining and acquiring props is generally called the property master. 
Most props are ordinary objects. Some may require modification, such as rewiring of lamps to be compatible with dimmers or painting to make an object look used or be more visible from front of house under bright or dim lighting.
Props may also be manufactured specially for the production. This may be for reasons of weight, durability and safety or the item may be unique in appearance and/or function.
A prop weapon, such as a gun or sword, can be a replica, a real weapon or a real weapon which has been modified to be non-functional.
To make melee weapons non-functional, swords often have their edges and points dulled. Knives are often made of plastic or rubber or have retractable blades.
It is common for functioning firearms to be used in film and television productions usually firing blanks.
Due to the increased level of risk it is standard practice for the safe and proper handling and use of firearms as props to be overseen by a specifically trained and licensed professional, usually called the weapons master or armourer. 
Although blank cartridges do not fire projectiles, they still have an explosive charge and can cause fatal injury.
Breakaway props are designed to be destroyed or break in use, such as furniture made from balsa-wood or cardboard and windows, bottles and glassware made from sugar glass or resin.  Cups, plates or vases may be made from bisque or wax. 
Although these are relatively safe a stunt double may replace the main actor for scenes involving their use.
Hero props are the more detailed pieces intended for close inspection by the camera or audience. The hero prop may have legible writing, lights, moving parts, or other attributes or functions missing from a standard prop.
A hero prop phaser from the Star Trek franchise, for example, might include a depressible trigger and a light-up muzzle and display panel (all of which would make the hero prop more expensive and less durable).
The term is also used to describe items used by the main character.
Although real money can be used,  when large quantities are required or the money is to be destroyed, it is usually more practical for facsimiles to be used, which are made to not only look realistic but also comply with counterfeiting laws. 
In recent years, the increasing popularity of movie memorabilia has elevated many props to the status of prized collectors items. "Screen-used" props can fetch vast sums at auctions and charity benefits.  
- Stembridge Gun Rentals, a major supplier of prop firearms to the US movie and television industry from 1920 to 2007
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