Whilst I know that technically it means two or a pair, I have always used it to infer between 2-4.
Perfect example is when someone says that they are popping to the shops to pick up a couple of things, they almost never mean only 2 items.
For me:
Couple = 2-4
Few = 4-6
Several = 7-9
Many = 10+
But it's usage is as subjective as it is contextual.