An apology is an admission of discourtesy or error together with an expression of regret. An excuse is a statement made or reason given for being released from blame. An apology accepts guilt and seeks to make amends; an excuse seeks to shift blame, deny guilt, and avoid censure: "Please accept my apology for neglecting to send you an invitation." "His excuse for being late is that his alarm clock failed to go off." Does one correctly say "Excuse me" or "Pardon me"? The former is a weaker expression than the latter, which implies guilt and a request for forgiveness."Excuse me" is the correct term to use when asking someone to be allowed to pass or to overlook a minor matter."Excuse me" should be used many times more often than "Pardon me," which is usually an expression of mistaken gentility and affectation.
Dictionary of problem words and expressions. Harry Shaw. 1975.