>At first sight we might imagine that knowledge could be defined as 'true belief'. When what we believe is true, it might be supposed that we had achieved a knowledge of what we believe. But this would not accord with the way in which the word is commonly used. To take a very trivial instance: If a man believes that the late Prime Minister's last name began with a B, he believes what is true, since the late Prime Minister was Sir Henry Campbell Bannerman. But if he believes that Mr. Balfour was the late Prime Minister, he will still believe that the late Prime Minister's last name began with a B, yet this belief, though true, would not be thought to constitute knowledge.
[1] THE PROBLEMS OF PHILOSOPHY https://www.gutenberg.org/files/5827/5827-h/5827-h.htm#link2...
I think that’s the definition of belief: it’s not derived from facts so it can’t be shaken by evidence.