Complex sentence: A conveyor belt (or belt conveyor) consists of two or more pulleys, with a continuous loop of material-the conveyor belt-that roled the drive pulley while the unpowered pulley is called the idler.
Split into simpler sentences: A conveyor belt (or belt conveyor) consists of two or more pulleys, with a continuous loop of material-the conveyor belt-that rotates about them. The powered pulley is called the drive pulley while the unpowered pulley is called the idler.