Trafalgar Day is the celebration of the victory won by the Royal Navy, commanded by Vice-Admiral Horatio Nelson, over the combined French and Spanish fleets at the Battle of Trafalgar on 21 October 1805.
At a Trafalgar Night banquet or dinner, a speech is usually made by a guest of honour who ends it with a toast to "The Immortal Memory ..." (The rest of the wording of the toast varies depending on what is said in the speech).
"The Immortal Memory of Lord Nelson and those who fell with him"