IWIM
Internet-based shorthand for "Is What I Meant."

May have extra letters added for emphasis, e.g. "IEWIM" would be 'is exactly what I meant', "IWIFM" 'is what I fucking meant", and others.
Somewhere on Tumblr:

"yah! IWIM!"
"wait, what?"
"it means 'what I meant', stupid"