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1. To quit or abandon (something), especially a career, endeavor, or enterprise. A noun or pronoun can be used between "jack" and "in." Primarily heard in UK. We're going to have to jack this project in if we can't secure more funding. After two years, Janet was ready to jack in her job at the firm.
2. To insert an electronic device or component (into something else) in order to form a connection. A noun or pronoun can be used between "jack" and "in." The new design means you can no longer jack in your headphones to the phone itself. You'll need an expensive adapter if you want to do that. You can jack up to three USB devices in at once along the side of the computer.
3. To interface one's brain with a computer system. Usually used in science fiction. The only way to access the mainframe is to jack in and manipulate the code from the inside. The café operates as a front for an illegal tech den where trans-humans jack in to live second lives in a virtual world.
See also: jack
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.