[blauekapelle]

Open source: source is freely available online.

Free software: free for modification, expansion or forking. Possibly free for profit (BSD license)

Source Available: Source is available but under restrictions. Locked room source viewing under NDA to confirm there aren't vulnerabilities for example.

[StavrosK]

Open source/free software: You can download, modify and re-release the source.

Source-available: You can view the source, perhaps freely, but can't modify or release your modifications.