It seems that a large majority of the general population is confused as to exactly what open-source is. There is a widespread misconception that open-source and public domain are synonymous when talking about software, Linux in particular.
Nothing could be further from the truth, and understanding the difference is crucial, not just to programmers, but to the general public. While there may be some disagreements on the topic of intellectual property, the fact that Linux, and all open-source code, depends on copyright law should assuage any fears that� Linux is anti-capitalist.
The GNU General Public License (GPL) is a widely used open-source license, and covers most parts of the Linux kernel. The GPL binds the recipient of open source software to a set of restrictions governing the ongoing licensing of the open source software.
Public Domain software (or anything else, for that matter, have, by definition, no restrictions placed on the use by the public at large. Because most open-source software is covered by the GPL or a similiar license, it cannot be considered public domain.
These are the ramblings of 
How does that relate to someone who wants to use Public or Open Source commercially?
Just trying to understand the differences.
elamb,
The GPL, and other open-source licenses, have certain restrictions that go along with them, particularly their “viral” properties in which code based on or incorporating GPL’d code is also automatically under the GPL. You cannot make closed source products out of open-source code.
Public domain has absolutely no restrictions on it, by definition. You could take public domain code that was out on the internet, package it up and sell it for whatever you wanted without ever letting anyone see the code, or, indeed, telling them where it came from.