Tendency of a roller to throw off small droplets of paint during application.
Higher quality paints are formulated to minimise spattering. Using high quality rollers which have proper resiliency further reduces spattering. In some cases, a quality wall paint may be preferred for ceiling work, for maximum spatter resistance. Overloading the roller with paint will result in excess spatter, as will overworking the paint once it is applied to a substrate. Working in metre-square sections, applying the paint in a zigzag 'M' or 'W' pattern and then filling in will also lessen the likelihood of spattering.
Source: The Paint Quality Institute