Clapsticks or clappers are a type of drumstick or percussion mallet that are used to serve the purpose of maintaining rhythm.
Unlike drumsticks, which are generally used to strike a drum, clapsticks are intended for striking one stick on another.

Music stick

As an ancestral instrument that traditionally accompanies the didgeridoo, it is sometimes referred to as musicstick or just Stick. In the language of the Yolngu Aborigines of Northeast Arnhem Land, Australia these clapsticks are called bimli.

It is used by Kate Bush (together with the didgeridoo) on her album The Dreaming.

Recording signal device

See Clapperboard

A clapstick is also a piece of equipment used in the motion picture and TV industry to signal a synchronization point on film and audio track. Since the audio is often recorded separately, the clapstick snapping shut is used to provide a single spot in the film where there's a distinct noise and a visual cue (the closed clapstick) to put the two tracks together.

A clapstick is usually striped and may be mounted on top of a slate which contains the scene information. Modern movie-making uses electronic synchronizers instead of clapsticks, but clapsticks are still a popular and inexpensive choice for the budget-minded film-maker.

References

• aboriginal.com.au