"Estimated Time to Arrival (ETA)":
Originally used on displays at train stations and airports ("ETA: hh:mm" indicating the expected arrival time), the term ETA made its way via some classic UNIX command line tools (e.g. ftp, where "ETA: X seconds" indicates the remaining up- or download time) into (UNIX-) nerd speech.

The Urban Dictionary ("ud": either in the WWW or via the SFOS app "Unofficial Urban Dictionary") should provide you with most such nerd language explanations.