A piano sonata is a sonata written for a solo piano. Piano sonatas are usually written in three or four movements, although some piano sonatas have been written with a single movement (Scarlatti, Scriabin, Medtner), two movements (Haydn), five (Brahms’ Third Piano Sonata) or even more movements. The first movement is generally composed in sonata form.
Beethoven: Piano Sonata No. 14 in C♯ minor, Op. 27 “Moonlight”