The so-called new BSD license applied to FreeBSD within the last few years is effectively a statement that you can do anything with the program or its source, but you do not have any warranty and none of the authors has any liability (basically, you cannot sue anybody). This new BSD license is intended to encourage product commercialization. Any BSD code can be sold or included in proprietary products without any restrictions on the availability of your code or your future behavior.
Do not confuse the new BSD license with “public domain”. While an item in the public domain is also free for all to use, it has no owner.