A casual shortened form of 'itterasshai' used as a farewell ('take care' / 'see you') when someone leaves.
「行ってきます」「いってら！」
"I'm off!" — "Take care!"
朝、友達を見送るときに『いってら』と言った。
In the morning I said 'ittera' when seeing my friend off.
急いでいる同僚に『いってら』とだけ声をかけた。
I just called out 'ittera' to my colleague who was in a hurry.