A spectrograph is an instrument that separates light into a frequency spectrum and records the signal using a camera. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves. The term was first used in 1876 by Dr. Henry Draper when he invented the earliest version of this device, and which he used to take several photographs of the spectrum of Vega. This earliest version of the spectrograph was cumbersome to use and difficult to manage.
One way to define a spectrograph is as a device that separates light by its wavelength and records this data. A spectrograph typically has a multi-channel detector system or imaging system that detects the spectrum of light. Wikipedia, Spectrograph