EULA: End User Licensing Agreement
Each piece of code a developer makes available should come with a EULA. This license is a piece of documentation which makes it clear what rights the developer retains and what rights the user has.
Within the internet community developers sometimes use a boilerplate license such as:
[add others here]
DKF: It should be noted that the legality of many commercial EULAs are distinctly dodgy, but the BSD license (which Tcl uses) is hard to dispute because it is very permissive.
LV: It should also be noted that while many times developers come to Tcl using GPL or LGPL as their license, that tends to start a political/legal discussion based on others requesting a change/addendum to using BSD/Tcl style licensing so they can use the code places where GPL/LGPL may cause some issues.
This page is NOT intended to be a place to debate these issues - I'm just making a general observation.