Sentence:  First, there are more than 300 ceramic wasters distributed throughout the deposit, as well as small numbers of burned and <WSD>overfired</WSD> sherds and badly deformed vessels. Some vases could not be fitted together properly, presumably because they had been broken during firing, and their parts subsequently had been warped .... 
Meaning of the word marked with <WSD> tags:  Fired at a high (or excessively high) temperature.