Denial Of Service.
You might be too new to this, but many of this type of attacks are becoming common and the most common target for this is Twitter. So what actually is this attack? In simple terms we can say that making false service requests just to de stabilize the system. For example we are using the help line to get help and when we do that constantly without any need of a help we create trouble and would block another user who is in really need of the service.