Polymethyl methacrylate is also known as Plexiglas (registered trade mark), but can also be referred to as acrylic. It is resistant and translucent. In some industries it is often used as an alternative to glass.
The ABS is a plastical material often employed by companies for its rigidity, its low weight, the easy way it can be modulated and its resistance to impacts. It can even be used on some car piece and remains the principzl material of Lego bricks.
An armrest is the horizontal part which is above the seat back, the armchair, the sofa... Their form and length can be different and the coating are different according to the furniture style.