Polarisation in nature

Although light allows us to see the world around us, it turns out that we may not always be getting the full picture. There are three fundamental aspects of light: brightness, colour and polarisation. As humans, we tend only to be familiar with the first two because while we can tell differences between light and dark and discriminate colours, we cannot see the polarisation of light. However, there are animals that can, whose eyes give them the ability to see the polarisation of light alongside its colour and brightness. So what is polarisation vision and what information can it give to these animals that is hidden from our eyes?