What does "open" mean in science? I understand that open science is based on open data, open access, open source, open methodology, etc.

However, what does "open" exactly mean in context when we talk about "open science"?
"Transparent"

If I had to condense the meaning of open in open science to a single word, it would be transparent.

The primary purpose of having open source software, accessible data, open access publishing, permissive licensing, and all of the other things we associate with open science, is to "open up" the scientific process as much as possible: allowing and enabling free and anonymous scrutiny of research outputs and the process that produced them, and for the repurposing of those outputs and processes for new research.