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Wiktionary
f major

n. 1 (context music English) The major key with the notes F, G, A, B♭, C, D, E, the key signature of which has one flat. 2 (context music English) The major chord with a root of F.

Wikipedia
F major

The F major scale (or the key of F) consists of the pitches F, G, A, B, C, D, and E. Its key signature has one flat.

Its relative minor is D minor and its parallel minor is F minor.

F major key is the home key of the English horn, the basset horn, the horn in F, the trumpet in F and the bass Wagner tuba. Thus, music in F major for these instruments is written in C major key. Most of these sound a perfect fifth lower than written, with the exception of the trumpet in F which sounds a fourth higher. (The basset horn also often sounds an octave and a fifth lower.)