Top Definition
"I'm in" is an alternate form of "count me in" which means "include me"
- I'm feeling hungry, so I'm going to order pizza. Who's in?

- I'm in
by Siemprejorge August 08, 2014

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A word used by side-acting hackers in movies when they have access to the mainframe.

Nothing can stop them now.
*vigorously types into the CMD prompt with green text color then presses enter*

I'm in.

I'm in the mainframe.
via giphy
by bighandednigga June 03, 2017

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