Skype and Adobe Reader, which can be used free of cost but whose source code is not released, are called:

1. Free and Open Source Software releases both the program and its source code to the public. 2. Sometimes software is freely available for use but the source code may not be available. 3. Such software is called freeware, and Skype and Adobe Reader are the standard examples. 4. Proprietary software must be purchased from the vendor holding the copyright. 5. So free to use does not by itself mean open source. _Source: syllabus Computer Science Class 11, Ch 1 'Computer System', S1.7.5 Proprietary or Free and Open Source Software_