What is what does certainly means?

Certainly means something that is definite, true, or accurate. It indicates a high degree of probability or likelihood, without any doubt or uncertainty. It is often used as an adverb to express agreement, affirmation, or permission, to indicate an affirmative answer or response, or to show confidence in one's statement or opinion. For example, "I am certain that I locked the door before leaving" or "Certainly, you can borrow my car if you need it."