There are 2 models of software licensing available to end users for software installed on their hosted desktop. Standard commercial licensing and open source. Each individual product may have its own nuances in regard to licensing and it is the sole responsibility of each user to determine the need for a license. Below are some general guidelines for licensing which you should be familiar.

Proprietary Software License

The hallmark of proprietary software licenses is that the software publisher grants a license to use one or more copies of software, but that ownership of those copies remains with the software publisher (hence use of the term "proprietary"). One consequence of this feature of proprietary software licenses is that virtually all rights regarding the software are reserved by the software publisher. Only a very limited set of well-defined rights are conceded to the end-user. Therefore, it is typical of proprietary software license agreements to include many terms which specifically prohibit certain uses of the software, often including uses which would otherwise be allowed under copyright law.

The most significant effect of this form of licensing is that, if ownership of the software remains with the software publisher, then the end-user must accept the software license. In other words, without acceptance of the license, the end-user may not use the software at all.

One example of such a proprietary software license is the license for Microsoft Windows. As is usually the case with proprietary software licenses, this license contains an extensive list of activities which are restricted, such as: reverse engineering, simultaneous use of the software by multiple users, and publication of benchmarks or performance tests.

Source: wikipedia.org

Open Source Software License

With a free software license, in contrast to proprietary software licenses, ownership of a particular copy of the software does not remain with the software publisher. Instead, ownership of the copy is transferred to the end-user. As a result, the end-user is, by default, afforded all rights granted by copyright law to the copy owner. Note that "copy owner" is not the same as "copyright owner". While ownership in a particular copy is transferred, ownership of the copyright remains with the software publisher. Additionally, a free software license typically grants to the end-user extra rights, which would otherwise be reserved by the software publisher.

With a free software license, in contrast to proprietary software licenses, a primary consequence of the free software form of licensing is that acceptance of the license is essentially optional -- the end-user may use the software without accepting the license. However, if the end-user wishes to exercise any of the additional rights granted by a free software license (such as the right to redistribute the software), then the end-user must accept, and be bound by, the software license.

Open source licenses generally fall under two categories: Those that aim to preserve the freedom and openness of the software itself ('copyleft' licenses), and those that aim to give freedom to the users of that software (permissive licenses).

An example of a copyright Free Software license is the GNU General Public License (GPL). This license is aimed at giving the end-user significant permission, such as permission to redistribute, reverse engineer, or otherwise modify the software. These permissions are not entirely free of obligations for the end-user, however. The end-user must comply with certain terms if the end-user wishes to exercise these extra permissions granted by the GPL. For instance, any modifications made and redistributed by the end-user must include the source code for these, and the end-user is not allowed to re-assert the removed copyright restrictions back over their derivative work.

Examples of permissive free software licenses are the BSD license and the MIT license, which essentially grant the end-user permission to do anything they wish with the source code in question, including the right to take the code and use it as part of closed-source software or software released under a proprietary software license.

Source: wikipedia.org