What is the characteristic of the JT65 mode?

JT65 is a digital protocol developed by Joe Taylor (K1JT) originally intended for Earth-Moon-Earth (EME) communications and later widely adopted for weak-signal HF operations. Its defining characteristic is its ability to decode signals with a very low signal-to-noise ratio. In fact, JT65 can reliably decode signals that are completely inaudible to the human ear and buried deep beneath the receiver's noise floor. The '65' in its name refers to the 65 discrete tones it uses for its multi-frequency shift keying (MFSK) modulation. It does not refer to a 65 Hz bandwidth or a 65 baud symbol rate, making those options clever but incorrect traps.