The courtroom definition of guilt is whatever a judge or jury says it is- as long as it’s proven “beyond a reasonable doubt.”
“Guilt” according to the dictionary is “the fact of having committed a breach of conduct especially violating law and involving a penalty.”
The key distinction from the courtroom version being the removal of the word “fact” and replacing with proof of the matter only “beyond a reasonable doubt”- something, quite obviously, less than having proven an actual fact.