A pinprick is what it sounds like — a tiny prick or hole created by something as small as a pin. People also use this word to represent something that is as annoying or irritating as the feeling of being pricked by a pin.
The word pinprick can evoke the image of something so tiny that it is the size of a pinprick, like seeing the stars in the sky as pinpricks of light. And then there is the sensation of a pinprick that is annoying and quick. This latter meaning has a metaphorical use, like when something refers to a tiny problem as a pinprick in comparison to more weighty troubles. No matter how you experience it, a pinprick is tiny. Don't sweat the pinpricks in life.