Occasional Chair, Feature chair, Arm chair, Lounge chair, same same. These are licence to assert some colour, design, and a piece of your character into the room be it via colour or design.
Unlike the sofa which is usually chosen for comfort, unless you’re buying a recliner with a remote control and a fridge in it, the living room chair balances the room and either adds that pop of colour it was lacking, offsets the simple design of the sofa with some style or adds a seat for you to melt into on your own.