specialized knowledge to read, but it is readable. In order for the application to actually run on a machine, it must be turned into a language that is understandable to the machine. The process by which the human-understandable form is translated into the computer-understandable form is called "compiling." Once the program has been compiled, it will run on a computer but is no longer readable by humans.
Most of the desk top applications we're familiar with such as Word, Excel, etc. are only available in compiled form -- Microsoft does not make the uncompiled version available. By contrast, open source software does include the uncompiled form so anyone can make additions or changes to it and compile it themselves. But, according to the Open Source Initiative, "open source" refers to more than just the handling of the application's code -- it also relates to the terms covering the way the application is distributed. Full details are available on the OSI site but the general concept is that open source software must remain open source and freely available to anyone for any purpose. If it is used as the basis for other products, those derivative products must, in their turn, abide by the open source distribution rules. This could have implications for agencies that use open source software as the basis for their own application development projects. In most cases, it will not be a problem but certain is an issue that needs to be considered.
So, though "open source" strictly speaking refers to the widespread availability of original developer work-product, it has come to mean much more as regards the ownership of software and the restrictions (or mandated lack of restrictions) on its distribution.