AT72 FLT CREW DEPARTING FROM VPS; MISUNDERSTANDS ATC COMMENTS AND CROSSED RWY HOLD LINE.

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WE WERE FLT 'ACR X.' WE HAD TAXI TO RWY 19 HOLDING SHORT AT TXWY P. THE TWR HAD TOLD US TO HOLD SHORT WAITING FOR LNDG TFC. AN ACR LANDED AND WAS ROLLING OUT. AT THIS TIME; THE FO AND I BOTH HEARD POS AND HOLD CONTACT CLRNC. THE FO READ BACK THE CLRNC AND REQUESTED PAST THE CABLE. THE TWR CAME ON AND SAID HOLD SHORT AT TXWY P AND CONTACT CLRNC. THE FO TOLD THE TWR THAT WE HAD ALREADY CROSSED THE LINE. THE TWR TOLD US TO DO A 180 DEGS AND HOLD SHORT AT TXWY P. ANOTHER CTLR CAME ON AND SAID WE COULD TAXI DOWN THE RWY IF NEEDED. WHILE WAITING; THE FO AND I TALKED ABOUT WHAT HAPPENED. MAYBE; HE SAID 'POS HOLD' AND NOT 'POS AND HOLD' AND WITH THE JET ON ROLLOUT 'POS AND HOLD' WAS WHAT WE WERE WAITING OR EXPECTING TO HEAR. SUPPLEMENTAL INFO FROM ACN 618459: AFTER DISCUSSING THE COURSE OF EVENTS WITH THE CAPT; WE BOTH AGREED THAT WE HAD HEARD THAT TWR CTLR SAY 'ACR X; POS AND HOLD...' HOWEVER; AFTER THINKING ABOUT IT; WE THOUGHT THAT THE CTLR MIGHT HAVE SAID 'ACR X; POS HOLD' MEANING FOR US TO HOLD OUR POS AT THE TXWY P; THEN TO CONTACT CLRNC DELIVERY BECAUSE THEY HAD A NEW EDCT TIME FOR US. THE CTLR SHOULD HAVE SAID; 'ACR X CONTINUE HOLDING SHORT OF RWY 19 AT TXWY P; CONTACT CLRNC DELIVERY ON...' OR; SIMPLY 'ACR X; WE HAVE A NEW EDCT FOR YOU; CONTACT CLRNC DELIVERY ON...' I KNOW THERE IS A LOT OF TRAINING AT THE EGLIN FACILITY; AND THE FACT THAT THERE WAS A SECOND TWR CTLR WHO OVER-STEPPED THE FIRST ONE LEADS ME TO CONCLUDE THAT THE FIRST CTLR WAS NEW. HE GAVE US A CONFUSING AND MADE-UP INSTRUCTION TO 'POS HOLD;' WHICH SOUNDS TOO MUCH LIKE 'POS AND HOLD.' HE SHOULD NOT HAVE DONE THAT.