Why JT65 is one of the WSJT family of weak-signal modes Joe Taylor developed for EME and other marginal paths. It sends a very slow 65-tone MFSK signal (about 2.7 symbols per second) in fixed one-minute transmissions with heavy Reed-Solomon forward error correction and rigid, compressed message formats. That combination lets the software pull a callsign, grid and report out of a signal roughly 25 dB below the noise in a 2500 Hz bandwidth, far weaker than the ear can hear.
Watch out The tempting picks read the 65 as a bandwidth or baud figure, but it is the number of tones; JT65 occupies only about 178 Hz and its symbol rate is under 3 baud.
The 65 in JT65 counts tones, not hertz or baud. What it buys you is decoding way down in the noise.