A CE425 ATP OBSERVER-PAX; DURING LNDG ROLLOUT AT LGB; RPTED THAT HE AND THE PF WERE CONFUSED BY TWR'S INSTRUCTIONS AND TAXIED OFF THE ACTIVE ONTO A CLOSED RWY RATHER THAN A TXWY.

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DURING THE ILS RWY 30 APCH TO LONG BEACH DAUGHERTY FIELD; WE WERE CLRED TO LAND AND HOLD SHORT OF RWY 25R. DURING THE ROLLOUT; THE CTLR ADVISED THAT WE WERE PASSING TXWY G AND THAT WE SHOULD TAKE THE 'NEXT ONE' AND CONTACT GND CTL ON 133.0. CONFUSION BEGAN WHEN IT WAS DETERMINED THAT THE NEXT EXIT POINT OFF OF RWY 30; AS INDICATED BY OUR UNDERSTANDING OF THE CTLR'S CLRNC WAS RWY 34L/16R; WHICH WAS CURRENTLY CLOSED FOR UNDETERMINED RWY END ZONE REPAIRS AND NOT ANOTHER TXWY AS WOULD BE EXPECTED. RWY 34L/16R WAS MARKED AS CLOSED WITH STANDARD STANDING X'S TO SIGNIFY ITS CLOSURE. BASED ON THESE CLOSURE MARKINGS AND THE GUIDANCE TO EXIT AT THE 'NEXT ONE;' OUR ACFT EXITED ONTO CLOSED RWY 34L/16R AND WE CONTACTED GND CTL ON 133.0; AS INSTRUCTED. UPON ESTABLISHING CONTACT WITH GND CTL; THE CTLR STATED WE WERE ON A CLOSED RWY; THAT THIS WAS OK AND TO TAXI VIA RWY 34L/16R AND TXWY G TO FBO. IT WAS ACKNOWLEDGED THAT OUR ACFT WAS ON CLOSED RWY 34L/16R; THE TAXI INSTRUCTIONS WERE READ BACK AND FOLLOWED. THE REMAINING TAXI TO PARKING WAS UNEVENTFUL. CONFUSION RESULTED FROM THE USE OF NON-STANDARD PHRASEOLOGY; THE CLOSURE OF RWY 34L/16R; A FAILURE TO CLARIFY THE SIT; WHICH LEAD TO MISUNDERSTANDINGS AND MISCOMS AS TO THE INTENTION OF THE CTLR'S CLRNC. AS A RESULT; OUR ACFT EXITED OFF OF THE ACTIVE RWY 30 ONTO A CLOSED RWY WITHOUT A CLR PLAN OF ACTION ON THE PART OF THE CTLR OR THE FLT CREW. IN THE FUTURE; A FULL AND COMPLETE DETERMINATION OF THE CTLR'S GUIDANCE AND INTENTIONS; AS WELL AS A FULL AND COMPLETE CLARIFICATION OF ANY MISCOM; MISUNDERSTANDING OR UNKNOWN PHRASEOLOGY SHOULD BE QUESTIONED AND RESOLVED BEFORE PROCEEDING ANY FURTHER.