harp
Refers to the large stringed instrument. In Japanese, ハープ usually means the orchestral harp.
She plays the harp in the orchestra.
She plays the harp in an orchestra.
harmonica
Short for ブルースハープ (blues harp). Used especially in blues and folk contexts. Less common than ハーモニカ for the general instrument.
See also: ブルースハープ
He is good at playing the blues harp.
He plays the blues harp in a blues band.
I'm planning to perform on the harp at the concert.
glass harp
blues harp; Richter-tuned harmonica; 10-hole harmonica
Irish harp
From English 'harp'. The harmonica sense comes from 'blues harp'.