Credibility of the source is checking the degree of authenticity of a source
(You want to know how reliable is this information?)
There are multiple factors that can help to check its credibility:
Is the author of the source trusted?
Is the background of the source safe?
Is it a primary or secondary source?
Have the source become unaccurate or
obsolete due to time?
Is there any motive or signs that the source is biased?
Freedom of speech
Freedom of action
The Russian ruler that enlarged the Russian empire is Ivan IV the terrible.
I hope this helps