A script is code written in the language of an interpreter such as Tcl.
In Tcl, a script is a collection of 0 or more Tcl commands separated by semicolon or newline. Said commands can later be sourced if stored in a file, run from a command line invocation of a TCL interpreter, [eval]'ed from a variable, invoked as a part of a call-back, and possibly executed in other ways. A script often provides a [library for use by other scripts.
A script can be created dynamically, and then evaluated using [eval].
Scripts can also contain (or generate) code in another language, i.e. SQL, Perl, ksh, awk, or even C, which can then be handed off to to some other interpreter for evaluation. SQL is probably the most well-known example of this. When dynamically generating scripts for another language, it is necessary to be aware of possible injection attacks.