There are a LOT of styles and variables to the general “rails” systems available for photo & video work. The basic unit as you describe is primarily used in conjunction with matte box applications. These devices utilize rods and a base plate to hold up the matte box, keeping from adding weight/stress to camera lens.
Other types help support systems for prompters, and yet others are geared toward using ultra-large lens assemblies. The term “rails” also applies to a host of systems allowing for camera movement in various directions for smooth, steady truck and other shots.
Systems can start at hundreds of dollars and quickly jump into the thousands of dollars stratosphere.
