Public Domain is the concept of an object being "owned" by everyone, therefore giving everyone the right do with it as they wish to.

This most often applies to the source-code for an application, or code-snippet. The pertinence to LSL is obvious, I would hope.

In defense of the concept of Public Domain is the Free Software Foundation. They have created a license, by which creators may attempt to maintain the Public Domain nature of their work (The successful nature of this defense is debatable). The license mentioned is the GPL, or General Public License.

Related to the GPL, but different from it in that it inhibits the commercial use of an object or idea, is the LGPL or Lesser General Public License.