Functional Threshold Power (FTP) is the power output a cyclist can sustain for one hour, typically tested directly or estimated from a 20-minute test discounted by 5-10%.

“the function fun threshold power or FTP is the power that you can hold for 1 hour that is one way to test it you literally get on a bike usually on an urg so it's it's a stationary bike — and you ride as hard as you can without blowing up for one hour and whatever the average power is that you held as your FTP much more typically — for example when I was a cyclist we would do this in a 20 minute test and we would discount it by typically 10% although Olaf suggested only 5% in my experience 10% was necessary”