APUs are AMD-speak for CPU and GPU on the same die (Intel has similar but doesn't call them that). Integrated graphics cards (a misnomer since there is no card -- IGP or iGPU is probably more accurate) may or may not be on the same die (instead could be on the motherboard, particularly in the chipset). That design is pretty rare/antiquated at this point though. Being on the same die means higher bandwidth, lower latency, etc.