A valediction is a speech that wishes a group of people farewell. It's most commonly given at graduations.
The word diction in valediction is a clue that this word has to do with speaking, since it comes from the Latin root dicere, "to say." When combined with valere, "be well," the result is valedicere, "bid farewell." Just about any type of school that has a graduation ceremony will have a valediction, which typically congratulates students on their accomplishments and inspires them to look ahead.