ACR RWY INCURSION. UNAUTHORIZED RWY XING.

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DUE TO THE ACFT GROSS WT; WE REQUIRED A SPECIAL IMPROVED FLAPS 1 DEP ON EITHER 17L OR 17R AT DENVER. TFC WAS DEPARTING 8L/R AND LNDG 17R/L. WE WERE GIVEN TAXI FROM OUR CONCOURSE E ON RWY 7 TO TURN L ON D3 TO HOLD SHORT OF Z. THEN WE WERE CLRED UP Z TO HOLD SHORT OF Z3. WE FIGURED THIS UNUSUAL RTING WAS TO AVOID SBOUND LNDG TFC OFF OF 17R AND WE ASSUMED WE WOULD BE USING 17R. THERE WERE RAINSHOWERS W AND N OF THE ARPT AND WIND SHIFTS AND WINDSHEAR LOOKED POSSIBLE. ONE CARRIER WENT AROUND ON 17R AS WE TAXIED UP Z. THEY STATED IT WAS DUE TO TURB. WE WERE CLRED TO CROSS Z3 TO 17. AN ACFT WAS JUST ROLLING S PAST Z3 AT THIS TIME. WE TURNED W TO CROSS 17R AND TWR CAUGHT OUR MISTAKE BUT NOT BEFORE OUR NOSE HAD CROSSED THE WHITE LINE. TWR TOLD SMALL TWIN Y TO GAR. THE ACFT ROLLING BY US AT THE TIME THE INSTRUCTIONS WERE GIVEN TO CROSS Z3 LED US DOWN THE WRONG PATH. EVERYTHING SEEMED TO FIT! THE KEY WORD 'CROSS' SHOULD BE RESERVED ONLY FOR RWY XINGS; NOT TO CROSS A TAXIWAY. PROPER TERMINOLOGY WOULD BE; 'CLRED TO CONTINUE NBOUND ON Z TO 17L'; WHICH IS WHERE ATC THOUGHT HE WAS SENDING US. YES; WE SHOULD HAVE QUESTIONED THE CLRNC! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: MADE STRUCTURED CALLBACK AS PART OF RWY INCURSION STUDY. RPTR EXPLAINED THE TERM 'SPECIAL IMPROVED FLAPS ONE DEP.' SAYS HE IS NOT SURE WHY THE FLC HAD A RWY 17R MINDSET OR WHY THEY DID NOT QUESTION THE CLRNC TO CROSS 17R. PREVIOUS CLRNC TO HOLD SHORT OF Z-3 WAS TO PROVIDE FOR ARR TFC LNDG 17L AND TURNING OFF AT Z-5 OR Z-4. NEED FOR LONGER RWY CAUSED ACR X TO TAXI OPPOSITE THE FLOW OF INBOUND TFC LNDG ON THE RWYS 17. RPTR CALL FACILITY AFTER FLT TO REVIEW WHAT HAD HAPPENED.