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.