A shell script is a computer program designed to be run by the Unix shell, a command line interpreter. The various dialects of shell scripts are considered to be scripting languages.
Typical operations performed by shell scripts include file manipulation, program execution, and printing text. A script which sets up the environment, runs the programme, and does any necessary cleanup, logging, &c is called a wrapper.
The term is also used more generally to mean the automated mode of running an operating system shell; in specific operating systems they are called other things such as batch files (MSDos-Win95 stream, OS/2), command procedures (VMS), and shell scripts, and mainframe operating systems are associated with a number of terms.