"The Charge of the Light Brigade" was a poem written by Alfred, Lord Tennyson, a British poet who lived in the 19th century. Its subject was an infamous British cavalry charge at the Battle of Balaclava during the Crimean War.
Just prior to entering battle during Operation Return against overwhelming Dominion and Cardassian forces, Miles O'Brien and Julian Bashir quoted a stanza of this poem. The quote had particular significance because the 600 Starfleet ships were in danger of being outflanked and surrounded by the larger Dominion fleet. (DS9: "Sacrifice of Angels")
Cannon to right of them,
Cannon to left of them,
Cannon in front of them
Volley'd and thunder'd;
Storm'd at with shot and shell,
Boldly they rode and well,
Into the jaws of Death,
Into the mouth of Hell
Rode the six hundred.