What is "Free Software"? What is "Open Source"? I will try to explain this in as simple a manner as possible.
Software is what does things for you when you use the computer. Otherwise it's just any other machine. To create software, we need to write codes. These codes are somewhat like English. For example :
This is meant to be an instruction to the computer to do this and do that. This is not real code, just a hypothetical example. Now this code cannot be understood by the computer. We need to convert this code to something that a computer can understand. This is what we call a program or software. If you have a piece of program, it is almost impossible to convert it back to its original code. However, code can be converted easily to software. Usually, when you buy/download a piece of software, you get only the part that the computer understands. You don't get the code that went into making of the software. Such kinds of software are called "propreitary" software.
Open source means that this code, or Source code, is available to anyone who wants it. Free Software means nearly the same thing, but is different. Note that "Free Software" and "Freeware" are completely different things.
The difference is in why they want the source code to be available. Those who believe in Open Source argue that making the source code available makes the software better. Their focus is on the developement of the software. Supporters of free software are more interested in the ethics of software. They believe that software should be free - free as in freedom, not free as in beer. Often , the terms are used interchangeably.
Watch this space for the rest of the explanation...