Its okay dont have to worry about expressing it wrongly, because I have great experience in trying to explain it.
Okay...Basically it is like it says, Attention Deficit/Hyperactivity Disorder. Horrible attention span, about 5minutes before I am completely bored, which is why I am currently on here, writing this whilst my teacher is walking around 'pretending to do my work'.
Hyperactivity, this is a hard one to explain, erm basically when your hyperactive, you are very very...hyper. You could always just go to something like Yahoo and search it there, there are like a billion sites that can explain it better then I can.