so, these two fans one says R where you would use this fan
CORSAIR iCUE Link RX120 MAX RGB 120mm PWM Thick Fans with iCUE Link System Hub – High-Static Pressure – Magnetic Dome Bearing – Triple Pack – Black
CORSAIR iCUE Link LX120-R RGB 120mm PWM Reverse Fans – Triple Fan Kit – Low-Noise, Magnetic Dome Bearing, Dual Light Loops, CORSAIR QuikTurn Screws, Zero
Those would be used on intake fans where you can see the fan blades.
It would mean that the air pushes into the case through the fan, and the side of the fan you would see from inside the case would be the side with the fan blades plainly visible. Normally, fans push air the other way (towards the side of the fan with the plastic support frame that holds the fan motor.) Using ones with “Reverse blade” design is the opposite.
You see this most often in cases like the King 95 Pro from Montech, where there’s a ton of glass all the way around, and the intake fans are plainly visible. They use reverse blade fans on those intakes so they look nicer.