C172 STUDENT AND INSTRUCTOR HAD A RWY INCURSION AFTER HEARING WHAT THEY THOUGHT WAS A 'LINE UP' CLRNC.

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AFTER RUN-UP; IN THE RUN-UP AREA AT THE END OF RWY 7 AT ORL; WE ADVISED GND WE WERE READY FOR THE TKOF. GND SAID TO MONITOR TWR. WE DID SWITCH TO TWR FREQ IMMEDIATELY. AFTER WAITING 5-10 MINS; I THINK I HEARD THE TWR'S INSTRUCTIONS TO 'LINE UP RWY 7.' I LOOKED AT MY INSTRUCTOR; HE SAID 'GO AHEAD.' WE THEN TAXIED JUST OVER THE HOLD SHORT LINE. AS WE DID A PLANE WAS LNDG MAYBE 100 FT DOWN THE RWY TO OUR L. I ASKED MY INSTRUCTOR; 'ARE WE SUPPOSED TO CROSS THE HOLD SHORT LINE?' HE SAID 'YES; THEY ARE VERY BUSY TODAY AND IS ANTICIPATING HIS ROLLOUT.' WE PROCEEDED ONTO THE RWY AND WERE CLRED FOR TKOF. AFTER RETURNING TO ORL AT XA30 LCL TIME; THE TWR CALLED MY FLT SCHOOL TO TALK TO MY INSTRUCTOR. MY INSTRUCTOR JUST LEFT FOR THE DAY; SO I CALLED THE TWR. THEY TOLD ME WHAT I DID WRONG; BUT SAID THAT IT WAS OK AND TO BE MORE CAREFUL. I WAS NOT FAMILIAR WITH THE TERM 'LINE UP;' IF THAT'S WHAT I HEARD; MY INSTRUCTOR MAY NOT HAVE BEEN FAMILIAR WITH THAT TERM EITHER. I DIDN'T HEAR 'HOLD SHORT RWY 7.' I AM RECEIVING MY FAR/AIM BOOK TO LOOK FOR THAT TERM; AND MUST BE MORE FAMILIAR WITH RADIO PHRASEOLOGIES.