1. A device used to light a stage, also known as a fixture by some. In the UK, the most common name is lantern. Probably the most correct name, and the one most used by manufacturers, is luminaire. In a realistic setting, instruments (PARs, Fresnels, Lekos, and so on) are not meant to be seen by the audience. When the fixture is seen (for example, a chandelier, a wall sconce, or the thing on your end table) by the audience, it is called a practical. 2. A tool: "surgical instrument" ex. scalpel; or device: "test instrument" ex. DMM or oscilloscope. 3. Apparatus for making music--band instrument: tuba; orchestra instrument: violin.