What is the meaning of this piece of Standardese about shared_ptr's use_count()?

Question

While trying to wrap my head around the problem shown in this question I found myself stuck on the following sentence from [util.smartptr.shared]/4:

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Answer 1

It means that the code in use_count() is either lock-free or uses mutexs to lock critical sections. In other words you can call it from threads without worring about race conditions.