Free software or libre software is software that can be use, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with minimal restrictions only to ensure that further recipients can also do these things. In practice, for software to be distributed as free software, the human readable form of the program (the "source code") must be made available to the recipient along with a notice granting the above permissions. Such a notice is a "free software licence", or, in theory, could be a notice saying that the source code is released into the public domain.