That phrase is actually one word in the original Greek: tetelestai.
The root of this word is “teleo” which means “to complete” or “bring to an end” and while the word may be unfamiliar to us, those who lived in first-century Palestine would have heard it spoken several times a day and in a variety of contexts.
For example, a servant would say “tetelestai” to his master when the task assigned to him had been completed and a hellenized priest might say “tetelestai” after examining a sacrificial lamb to determine its perfection.
Perhaps the most striking use of the word “tetelestai” in Jesus’ day was in commercial and judicial contexts.
After a debt or tax bill had been paid, the word “tetelestai” would written on the receipt. The modern equivalent would be the “paid in full” stamp.
When a criminal was released after fulfilling his sentence, the word “tetelestai” would be written on the original charges. Sometimes a “tetelestai” sign would even be nailed to the door of his house so the townspeople would know that he had fully paid for his crimes and was now a free man.
Therefore, when Jesus said “tetelestai” from the cross, he was indicating that the work of redemption had been completed, that our sin debt had been paid in full, and that we were now set free from the prison of hell.