ftone or f-tone, noun,
the f-tone, middle "F" on the piano, is considered by physicists to be the tonic of nature.
f-tone is associated with the fourth, green, heart chakra.
noun - used as a mantra for meditation.
A person might play the ftone and hold that note so it plays a constant middle "f". They would then use the constant tone for a mantra to assist them in their practice of meditation.