An alphabet is a standard set of letters written to represent particular sounds in a spoken language. Specifically, letters correspond to phonemes, the categories of sounds that can distinguish one word from another in a given language. Not all writing systems represent language in this way: a syllabary assigns symbols to spoken syllables, while logographies assign symbols to words, morphemes, or other semantic units.
A photo of the Old Hungarian script
Ge'ez Script of Ethiopia and Eritrea
In a writing system, a letter is a grapheme that generally corresponds to a phoneme—the smallest functional unit of speech—though there is rarely total one-to-one correspondence between the two. An alphabet is a writing system that uses letters.
Ancient inscription on a vase featuring Greek letters
The American manual alphabet, an example of letters in fingerspelling
Engravings of decorated Latin letters, from the 18th century (note the lack of a J and a U)
Image: Decorated Roman alphabet MET DP855610