Adapter / splitter (?)

I have a cable which plugs into my charging port which then has a usb slot on the end. I want to watch films on my tablet which I can now do but I also need to be able to charge the tablet at the same time. Is there some kind of double socket I can plug into the charger point that I can then use to plug the charger and my existing usb cable into use both at the same time? What would this be called, I've tried searching splitters and adapters but this only seems to come up with car chargers which is not what I need.

Thanks!