Is what is meant by "harf" in the Prophet's (peace be upon him) saying: "Whoever recites a harf from the Book of Allah will have a good deed thereby," a letter of the alphabet or a word?

Reciting the Quran is a great act of worship. The reciter receives ten good deeds for each letter, as the Prophet, peace and blessings be upon him, said: "Whoever recites a letter from the Book of Allah will receive a good deed, and a good deed is multiplied tenfold. I do not say that 'Alif-Lam-Mim' is one letter, but rather 'Alif' is a letter, 'Lam' is a letter, and 'Mim' is a letter." The intended "letter" is an alphabetical letter.