In relation to programming languages, script refers to the non-compiled interpreted portion of a program.
In relation specifically to TCL, _a_ script is a collection of commands saved in a file for later use as an application or library. It can later be sourced or run from a command line invocation of a TCL interpreter.
Actually, the storage in a file is optional. Any valid sequence of 0 or more Tcl commands is often called a script, whether it was read from a file, pulled from a database, or constructed on the fly.