This is the SCSI status byte as defined by the SCSI standard. Note that it can have vendor information set in bits 0, 6 and 7 (although this is uncommon). Further note that this 'status' data does _not_ match the definitions in <scsi/scsi.h> (e.g. CHECK_CONDITION). The following 'masked_status' does match those definitions.  The type of status is unsigned char .
Some lower level drivers (e.g. ide-scsi) clear this status field even when a CHECK_CONDITION or COMMAND_TERMINATED status has occurred. However they do set DRIVER_SENSE in driver_status field. Also a (sb_len_wr > 0) indicates there is a sense buffer.