Shell Glossary
A command interpreter that sits between a user or agent and the operating system.
Shell
A shell is a command interpreter that sits between a user or agent and the operating system.
You give the shell a command; it parses the instruction, finds the requested program, starts it, connects its input and output, expands variables or wildcards, and returns the result. Bash and zsh are shells. PowerShell is a shell in the Windows ecosystem.
The name comes from the idea that the shell surrounds the operating-system kernel. It is an interface to the system, not the system itself.
A shell can be used interactively through a terminal or non-interactively by an application, automation job, or AI agent. This is why an agent can “run a shell command” without a terminal window appearing on the screen.