A spec light is one which only contributes specular components to the render e.g. you turn off diffuse calculations for the light.
And by specular lighting map do you mean just a regular spec map? if so it's just a greyscale map of where spec is allowed to happen and where it's not. It's essentially a multiplier so white being 1 and black being 0. so for example you have a piece of geo which has a spec hit on it. if your map says that this area is black then it gets multiplied by 0 and thus the spec component is removed (remember that anything x0 == 0)
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