RWY INCURSION BY A B737-300 FLC WHEN THEY MISINTERP THE CLRNC AND WHERE TO HOLD SHORT OF RWY 9L AT ORD; IL.

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TAXIING OUT TO TKOF. GOT ASSIGNED RWY 9L. HAD WT PROB AND NEEDED 'KID COUNT.' TOLD TWR WE NEEDED SOME TIME; SO TWR GAVE INSTRUCTIONS TO GET US OUT OF THE WAY UNTIL WE WERE READY. BOTH PLTS UNDERSTOOD CLRNC TO CROSS RWY 9L; DO A 180 DEG TURN AND HOLD SHORT OF RWY 9L AND SAY WHEN WE WERE READY. WE TURNED ON APPLICABLE LIGHTING AND CROSSED RWY 9L AFTER CHKING FOR TFC. AFTER XING; WE WERE TOLD THAT HAD NOT BEEN OUR CLRNC AND WERE TOLD TO DO A 180 DEG TURN AND HOLD SHORT AGAIN ON TXWY J; N OF RWY 9L. TWR SAID 'NO PROB.' WE THINK THE CONFUSION MAY HAVE STEMMED FROM HEARING TWR SAY 'TAXI STRAIGHT AHEAD' WHEN WE WERE HOLDING SHORT OF RWY 9L FACING N ON TXWY J. WE THINK HE MAY HAVE THOUGHT WE WERE FACING E ON TXWY H INSTEAD; BUT CANNOT BE SURE WHAT HE PERCEIVED. UNEVENTFUL AFTER THIS POINT THROUGH TKOF AND DEP. SUPPLEMENTAL INFO FROM ACN 564051: ALTHOUGH THE WORKLOAD WAS FAIRLY HIGH DUE TO THE WT DISCREPANCY; BOTH PLTS WERE LISTENING TO ATC INSTRUCTIONS; AND BOTH PLTS UNDERSTOOD THOSE INSTRUCTIONS TO 'TAXI STRAIGHT AHEAD; CROSS RWY 9L; DO A L 180 DEG TURN AND HOLD SHORT ON TXWY J FOR RWY 9L.' FO ACKNOWLEDGED AND READ BACK INSTRUCTIONS. CLRLY THIS WAS NOT WHAT TWR INSTRUCTED; YET IT'S WHAT WE BOTH UNDERSTOOD.