Jack in
Jack in turns up in 2 fields: electronics, telecom & it. Here is what it means to the people in each one.
Jack in in electronics
To physically connect a cable or plug into a receptacle.
To insert a physical connector, usually an audio or communication plug, into its corresponding socket to establish a link. The term originates from telephone switchboards and audio patch bays but is used loosely on the bench to mean hooking up any piece of test gear or peripheral.
"Jack in the logic analyzer so we can see what the bus is actually doing during boot."
Jack in in telecom & it
To physically connect a device to a network using a cable, or to log into a secure digital system.
To jack in means to establish a hardwired connection, usually by plugging an Ethernet cable into a wall port or switch. In hacker and IT culture, it also refers to authenticating into a remote server or virtual environment. The term originates from the physical action of inserting a patch cable into a telecom jack.
"Grab your laptop and jack in to the console port on that router so we can see the boot sequence."