"Ä", or "ä", is a letter, representing a vowel, in the Finnish, Swedish and Estonian alphabets. It also appears in the German alphabet, where it represents "A" with umlaut, and is alphabetized as though spelled "AE".
In German and Swedish, "Ä" is pronounced /E/ like the "ai" in hair.
In some English dictionaries, such as the Merriam-Webster Dictionary, the Random House Dictionary and the American Heritage Dictionary of the English Language, "ä" is used to represent the sound of the "a" in "father", though the International Phonetic Alphabet (used e.g. in the Oxford English Dictionary) represents that sound with a different symbol, ɑ.