Shell shoveling, in network security, refers to the act of redirecting the input and output of a shell to a service so that it can be remotely accessed.
In computing, the most basic method of interfacing with the operating system is the shell, on Microsoft Windows based systems this is a program called CMD.EXE or COMMAND.COM, on Linux or Unix based systems it may be any of a variety of programs such as bash, ksh etc. This program accepts commands typed from a prompt and executes them, usually in real time, displaying the results to what is referred to as standard output, usually a monitor or screen.
In the shell shoveling process, one of these programs is set to run (perhaps silently or without notifying someone observing the computer) accepting input from a remote system and redirecting output to the same remote system; therefore the operator of the shoveled shell is able to operate the computer as if they were present at the console.