No changes are made that would endanger the Sprint Goal.

The Scrum Guide on Page 7 says that -

During a Sprint:
- No changes are made that would endanger the Sprint Goal.
- Quality goals do not decrease; and,
- Scope may be clarified and re-negotiated between the Product Owner and Development Team as more is learned.

Can the experts help me understand the first item - No changes are made that would endanger the Sprint Goal.

The questions that comes to my mind is - No changes are made to WHAT?

Thanks

Robb