A shorthand for [incr Tk].

----
"ITK" is also an acronym for the US 
National Library of Medicine's
[http://www.nlm.nih.gov/]
open-source software, "Insight Segmentation and Registration Toolkit"
[http://www.itk.org].  This package supports the Visible Human Project
[http://www.nlm.nih.gov/research/visible/visible_human.html].

There's a high-quality binding of (this) ITK to Tcl.
----
[Category Package]