100% duty cycle is when compressors are able to deliver compressed air throughout their whole cycle time. But, it is important to note that this doesn't necessarily mean they're capable of continuous use unless it's specified. A compressor with a 100% duty cycle rating but not specified as being continuous use, will still need rest time otherwise you risk premature wear. On the other hand, a compressor with a 100% duty cycle rating and specified as being continuous use, can be used continuously without premature wear and will only rest when not in use.