Aitch is the letter H written out as a word, the way you write bee for B or ess for S. You need it when you are talking about the letter itself, not using it inside a word. In most of the United States, and in older British teaching, the name starts with a vowel sound: aitch. Though actually, a great many people — in Ireland, in parts of Britain, in Australia — say haitch, with an H at the front. Some teachers still mark haitch as wrong; many families say it that way at home without thinking. Neither group is foolish. In England there is an old social sting around this letter: dropping your aitches (saying ouse for house) used to mark a speaker as working-class, and that fight made people extra proud, or extra shy, about how they named H. The word itself is only the name of the letter.