A standard flyback design uses an optocoupler to feedback the output voltage information across the isolation barrier to the control IC. The regulator then uses this information as part of the control loop to regulate the output voltage.
A no-opto flyback is a modified version of this topology where the feedback mechanism is monitoring the output voltage by looking at the primary side waveform. This removes the need for the optocoupler and saves space, power and removes the reliability impact associated with optocouplers which can degrade over time.
Some popular examples of no-opto flybacks:
LT8300, LT8301, LT8302, LT8303, LT8304