A Smith machine is a piece of weight training equipment that consists of a barbell fixed within a vertical frame. This design allows the barbell to move only in a straight up-and-down path, providing stability and safety for users. It is commonly used for exercises like squats, bench presses, and shoulder presses, making it suitable for both beginners and experienced lifters. The Smith machine often features adjustable safety stops, which help prevent injury by catching the barbell if the user cannot complete a lift. This equipment is popular in gyms and fitness centers, as it allows for a controlled workout environment while still enabling users to lift heavy weights.