U+0100 Latin Capital Letter A with Macron

The Wikipedia has the following information about this codepoint:

Ā, lowercase ā, is a grapheme, a Latin A with a macron, used in several orthographies. Ā is used to denote a long A. Examples are the Baltic languages (e.g. Latvian), Polynesian languages, including Māori, some romanizations of Japanese, Persian, Pashto, Assyrian Neo-Aramaic (which represents a long A sound) and Arabic, and some Latin texts (especially for learners). In Romanised Mandarin Chinese (pinyin) it is used to represent A spoken with a level high tone (first tone). It is used in some orthography-based transcriptions of English to represent the diphthong (see Vowel length § Traditional long and short vowels in English orthography).

In the International Alphabet of Sanskrit Transliteration, Ā represents the open back unrounded vowel "आ", not to be confused with the similar Devanagari character for the mid central vowel, अ.

In languages other than Sanskrit, Ā is sorted with other A's and is not considered a separate letter. The macron is only considered when sorting words that are otherwise identical. For example, in Māori, tāu (meaning your) comes after tau (meaning year), but before taumata (hill).