Sentence:  It <WSD>is</WSD> , I am reliably given to understand , the technical argot for those who engage in your particular branch of the boost ; i.e. , burglars who rob while the tenants are absent , in contrast to hot slough prowlers , those who work while the occupants are home . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)