Piano and Organ

Those two often confuses me. Which one is the piano or which one is the organ? I was already in college when I could finally distinguish which is which when a relative would often shout jokingly to put something on top of the piano. There and then I realize that the big one is the piano and the small one we used to have was called an organ. It was broken now, I wonder if we could have it fix or just buy a musicians friend arranger keyboards. Either way, I want my kids to experience music using their hands, so we definitely are going to have a working organ in the house soon.