A software license is a legal instrument (usually by way of contract law, with or without printed material) governing the use or redistribution of software. Under United States copyright law, all software is copyright protected, in both source code and object code forms. The only exception is software in the public domain. A typical software license grants the licensee, typically an end-user, permission to use one or more copies of software in ways where such a use would otherwise potentially constitute copyright infringement of the software owner’s exclusive rights under copyright.
Free software is software that can be freely used, modified, and redistributed with only one restriction: any redistributed version of the software must be distributed with the original terms of free use, modification, and distribution (known as copyleft). The definition of free software is stipulated as part of the GNU Project and by the Free Software Foundation. Free software may may be packaged and distributed for a fee; the “free” refers to the ability to reuse it, modified or unmodified, as part of another software package. As part of the ability to modify, users of free software may also have access to and study the source code.
A full version software may also circumvent or serialize a piece of commercial software. Commercial software often uses keys to authenticate the user and software during installation. Without the key, the software is unusable. The full version software is used to get past this security feature by generating a key. Or, it may change a file to trick the software into allowing the to use it as if the correct product key had already been entered. The latter is the most distributed methodology for full version software licenses.