User's Guide Book: Overview --> Free (Libre) and Open Source Software (FLOSS)
First of all, I think we should use EU terminology, also - the main definitions of lead organisations (FSF, OSI, etc.).
- Free/Libre/Open Source Software, the term most commonly used when talking about either Free (Libre) Software or Open Source Software.
- Open Source Software is plain software, just like you know already. When in operation, you won't notice that the software is actually Open Source. The difference with its counterpart (proprietary software, also known as
closed source softwareor CSS) is the way in which it is licensed.
- Source code
- The human-understandable texts that programmers type to write applications.
What is Open Source Software? - http://europa.eu.int/idabc/en/document/1745/468
The Many Aspects of Open Source - http://europa.eu.int/idabc/en/document/1744/468
More info on terminology: Glossary.