In short, you don't lose your own copyright but you grant them a license to do whatever they want including re-license as they wish without having to ever consult you, allowing for your code to be used within their closed source projects under any license they wish.
In short, you don't lose your own copyright but you grant them a license to do whatever they want including re-license as they wish without having to ever consult you, allowing for your code to be used within their closed source projects under any license they wish.