Simplify the following text for a Grade 8 native English-speaking person.
Original: yiá aki , also sometimes spelt yirdaki , refers to the specific type of instrument made and used by the Yolngu people of north-east Arnhem Land .
Simplified: Yirdaki , also sometimes spelt yidaki , is for the instrument made and used by the Yolngu people of north-east Arnhem Land .