Isot stands for Island in the Sea of Time. It references a novel where an island in relatively recent times is taken from it's time and place, and placed in the distant past, creating an alternate history. The acronym is popular on the alternate history forum.
What if Darth Vader were ISOTed into Anakin just after his nightmares about his mother started?
"I can't wait to see my sister when she finds out who was with Mike last night"
"OH MY GAWD I TRUSTED YOU BITCH!"
"Hahaha that's great...even I can't imothate her that well"