“OTL” is one of the commonest acronyms used on AH.com and its discussion board. It simply means “Our timeline” - i.e., the history of the world as we know it, everything but the history of a fictional, parallel universe with alternate history properties.

AH.com's AH Writing Slang

ATL

ASB - The acronym for the concept of Alien Space Bats in the genre of alternate history.

ISOT - The acronym for personal or mass teleportation to other historical eras or other worlds/setting, usualy initiated via unexplained ASB means.