Clip sticks are extendable poles, with a clever head mechanism on the end, that enables the user to attach a quickdraw and clip the rope into the first (or even higher) bolt on a sport route, thus making the route safe from the outset. They are also useful when unable to climb a section of a sport route or when 'clipping-up' a route so that the climber can 'work' the route prior to attempting to lead it. The clever head design means that they can also be used with Beta/M-16 style nylon brushes for brushing those out of reach holds at the crag or in the climbing wall.
A recent introduction to the market are extendable poles designed entirely for brushing holds. These are most often used when bouldering to remove chalk, dirt and moisture from holds that are out of reach.