Open source software is defined by the open source licenses under which applications and code are made available. Have you ever wondered what the most popular open source licenses in use today are?

A new study from enterprise open source service provider OpenLogic, released today at the Open Source Business Conference (OSBC) reveals that the answer to what is the top open source license depends on how the question is asked.

When looked at from the perspective of total projects and the code under which they are licensed, 68.9 percent of open source software packages use the GPL. The Apache software license comes in second at 7.6 percent.

Adjusting the question to look at the top open source projects by download and what licenses they use, present a different view of the data. According to OpenLogic, measured by downloads the top open source license is the Apache License at 32.7 percent. The LGPL came in second at 21.0 percent and GPL is third at 14.4 percent.

"It's not surprising that people distributing open source tend to lean towards Apache and liberal licenses," Kim Weins senior vice president of products and marketing at OpenLogic told InternetNews.com. "It's a little more surprising to see that even downloads of open source are dominated by Apache-licensed projects."

OpenLogic provides support for open source projects listed on its OpenLogic Exchange (OLEX) service which lists some 330,000 projects. Weins noted that the top five open source projects that are downloaded from OLEX are Tomcat (Apache license), JBoss (LGPL), PHP(PHP Software License), MySQL(GPL v2) and Hibernate(LGPL).

"The license distribution of the Top 5 is less skewed toward Apache  which is associated with only 1 of the top 5," Weins said. "This indicates that the adoption of the Apache license is coming from a broad set of different projects."

Weins added that she suspects that the downloads of open source applications skews toward Apache because of the broad range of Apache projects for Java -- which sees heavy adoption in the enterprise.

"However, the preference to use Apache licenses in products that are distributed is also because of enterprise concerns that they might have to license their own code under a GPL license," Weins said.

With the GPL license, OpenLogic is tracking both GPLv2 and v3 versions of the license. According to Weins, the split between GPL license versions chosen by open source developers is roughly even. There are a similar number of packages under GPLv2 and GPLv3.

"However in the case of usage, we see 4x as many open source packages under GPLv2 being used as under GPLv3," Weins said. "This indicates that enterprise adoption of GPLv3 is lagging behind open source projects choosing GPLv3."

As cloud adoption begins to grow, there could be an effect on open source license usage in the future.

"A shift toward cloud computing could make the GPL licenses more acceptable in the enterprise, since most experts don't believe the cloud computing models will trigger the distribution clauses of the GPL license that tend to concern enterprises," Weins said. "However, many in the open source community would like to use the Affero GPL more heavily as a way to preserve the copyleft ideals of the GPL even when operating in a cloud computing environment."

Sean Michael Kerner is a senior editor at InternetNews.com, the news service of Internet.com, the network for technology professionals.