In an SSB/CW receiver, what is the purpose of the signal produced by the beat frequency oscillator (BFO)?

The Beat Frequency Oscillator (BFO) is a dedicated oscillator in a receiver that generates a steady, unmodulated radio frequency signal. Its purpose is to replace the carrier wave that was intentionally removed at the transmitter for SSB (Single Sideband) and CW (Continuous Wave) transmissions. To make the audio intelligible, the product detector mixes the incoming intermediate frequency (IF) signal with this BFO signal. The difference between these two frequencies results in the original baseband audio. Without the BFO reinserting this reference carrier, SSB voices would sound like incomprehensible 'duck talk' and CW signals would just be silent thumps. A common distractor is the Local Oscillator (LO), which mixes with the incoming RF signal to create the IF; the BFO, however, mixes with the IF to finally recover the audio.