oration：a formal speech made on a public occasion,especially as a part of a ceremony.
它就是讲说致辞的意思~（尤其作为意识的一部分）
speech：a formal talk that a person geives to an audience.讲说,讲话,发言.
discourse：a long and serious treatment or discussion of a subject in speech or writing.演讲,论文.
一般演讲用speech就行~