"Cloud amount" refers to the measure or degree of how much of the sky is covered by clouds. It tells us whether the sky is mostly clear with few clouds, partially covered with some clouds, or completely covered and cloudy. Full definition
Changes in cloud amount and cloud types might increase warming (positive feedback) or reduce it (negative feedback). (usask.ca)
Additional feedback from low cloud amount is also positive in most climate models, but that result is not well understood, nor effectively constrained by observations, so confidence in it is low. (fabiusmaximus.com)
The warming effect of clouds depends on cloud height and effective cloud amount, but also on atmospheric conditions like near - surface temperature and humidity. (pubs.giss.nasa.gov)