Introduced in 1.6 to support modifier terms within the metadata table, a non-null ('X') _M_EXCLUSION_CD_ indicates the modifier is to be excluded from the specified applied path. Traditional concept terms and non-exclusion modifiers have an M_EXCLUSION_CD of null.
An M_APPLIED_PATH of '\Diagnoses\Circulatory system%' and M_EXCLUSION_CD of 'X' means that the term is a modifier that is excluded from the term(s) with C_FULLNAME of '\Diagnoses\Circulatory system\' and all its descendants, whereas a M_APPLIED_PATH of '\Diagnoses\Circulatory system\' applies to the term with C_FULLNAME of '\Diagnoses\Circulatory system\' only.