Complex sentence: The last form shown, referred to as or "Kid Buu", is actually Boo's original, and appears when Gohan, Gotenks, Piccolo and the fat Boo are removed from his body.
Split into simpler sentences: The last form shown, referred to as is actually Boo's original form. He appeared when Gohan, Gotenks, Piccolo and the fat Boo are removed from his body.