The word "declamation" comes from the word declaim and means to make a formal speech. It is a noun that originated around the year 1550.
A declamation is typically used to protest or condemn something or someone. It is a very emotional speech designed to stir a strong reaction in people listening to it.
A famous example of a declamation was the speech that Brutus gave to the crowd after he helped murder Julius Caesar. He declaimed from the Roman senate steps and explained to the crowd why he'd helped murder Emperor Caesar.
Declamation also means speech or writing that is for oratorical effect or the correct enunciation of words.