Simplify the following text for a Grade 7 native English-speaking person.
Original: In blues music , the harmonica is casually referred to as a `` Blues harp '' or `` harp '' , but it is a free reed wind instrument , not a stringed instrument , and is therefore not an actual harp .
Simplified: The harp is such an old musical instrument , that people sometimes say harp when they mean any kind of instrument .