What is meant by the term "in a condition for safe operation?"
This is an initial determination by an FAA inspector or authorized Representative of the Administrator that the overall condition of an aircraft is conducive to safe operations. This refers to the condition of the aircraft relative to wear and deterioration, e.g., skin corrosion, window delamination/crazing, fluid leaks, tire wear, etc.

How does the FAA determine that an aircraft is in a condition for safe operation?
The FAA inspector or authorized Representative of the Administrator will make an initial determination as to the overall condition of the aircraft.  The aircraft items evaluated depend on information such as aircraft make, model, age, type, completeness of maintenance records of the aircraft, and the overall condition of the aircraft.