BFCM stands for Black Friday Cyber Monday - the peak retail weekend from Black Friday through Cyber Monday, and the biggest concentrated demand event of the DTC year. (You'll also see it written as BFCM weekend or the Cyber 5.) BFCM is won in the months before, not the week of: your list size, creative, inventory and fulfilment capacity are locked in long before the weekend. Discounting hard without protecting contribution margin is how brands buy record revenue and lose money doing it.
Benchmark. Plan inventory and fulfilment for 3-5x a normal week, and model the margin impact of your offer before you commit. A 'successful' BFCM that destroys contribution margin is not a win - revenue is vanity, profit is sanity.