pandas.DataFrame.is_copy has no description in the docs
#### Code Sample, a copy-pastable example if possible

https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.is_copy.html#pandas.DataFrame.is_copy

#### Problem description

It isn't clear what this property tells -- there's no documentation. When does it become true, and when does it become false?



#### Expected Output

#### Output of ``pd.show_versions()``
