Sentence:  The individual members of the cytochrome P450 superfamily are referred to using the nomenclative CYP (for the superfamily) plus a number identifying a <WSD>family grouping</WSD> of isozymes with a more than 40% homology of amino acid sequences (e.g., CYP2). 
Meaning of the word marked with <WSD> tags:  A group of related items.