WeatherTalk: When is a shower just a shower?
And when is it just plain old rain?
What makes a shower a shower as opposed to just plain old rain? The classic meteorological definition is that a shower is brief and/or intermittent, whereas rain is steady, but there is no specific time limit for when a shower lasts long enough or is steady enough to become rain. Meteorologists separate the two by their formation. A shower is convective, meaning it is caused by small-scale updrafts of air. General rain is caused by a general, gradual rising motion over a large area, producing a steadier, relatively long-lasting period of rainfall.
Here, again, the separation becomes vague. There is no cutoff at which rising air is of too large a scale to be considered a shower-making updraft. Fortunately, this is of no great matter. We speak loosely of rain, rain showers, thundershowers and thunderstorms in ways that make sense. To set hard boundaries between these words would serve no real purpose.