Rain with no great changes in its precipitation... ie. there's no change from a light shower to a full downpour - the rain is consistently heavy, light or in between.

A rain that comes down at the same rate and doesn't stop and start again. It doesn't start out heavy (for example), then change to a light rain and/or stop a number of times. It could be a light, medium or heavy rain. As long as it stays raining at the same rate, the way it started, it is a consistent rain.