ShellCode

Shellcode is basically a list of carefully crafted instructions that can be executed once the code is injected into a running application. Stack and heap-based buffer overflows are the most popular way of doing so. The term shellcode literally refers to written code that starts a command shell.

The remote shell (rsh) is a command line computer program that can execute shell commands as another user, and on another computer across a computer network. The remote system to which rsh connects runs the rsh daemon (rshd).

The command shell is a separate software program that provides direct communication between the user and the operating system. The non-graphical command shell user interface provides the environment in which you run character-based applications and utilities