A [Tcl] extension is a [library] of additional commands for a Tcl interpreter. Extensions are written in [C] using the Tcl [API], and are loaded into a running interpreter with [[`[load]`]. Extensions often distributed as part of a [package] that often includes [script%|%scripts%|%] to facilitate the use of the extension. An extension may define new actions, new [widget]s, new processing types, etc. ** See Also ** [Tcl Extension: User Guide]: [Tcl Extension: Developer Guide]: [Extensions for Tcl and Tk]: [Extending Tcl]: How to write software that will be implemented as an extension, perhaps in C (or C++ code with `extern "C" {}` around it). [Sampleextension]: [package]: [extension language]: <> Glossary