This character is a Decimal Number and is mainly used in the Meitei Mayek script. The codepoint has the decimal value 0. The character is also known as phun.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written from left to right. When changing direction it is not mirrored. This number joins with other adjacent letters and numbers to form a word. U+ABF0 forms a number with similar characters, which prevents a line break inside it.
The Wikipedia has the following information about this codepoint:
The Meitei script (Meitei: ꯃꯩꯇꯩ ꯃꯌꯦꯛ, romanized: Meitei mayek), also known as the Kanglei script (Meitei: ꯀꯪꯂꯩ ꯃꯌꯦꯛ, romanized: Kanglei mayek) or the Kok Sam Lai script (Meitei: ꯀꯣꯛ ꯁꯝ ꯂꯥꯏ ꯃꯌꯦꯛ, romanized: Kok Sam Lai mayek), after its first three letters is an abugida in the Brahmic scripts family used to write the Meitei language, the official language of Manipur and one of the 22 official languages of India. It is first known from engravings on 6th century AD coins. as verified by the various publications of the National Sahitya Akademi. It was used until the 18th century, when it was replaced by the Bengali alphabet. A few manuscripts survive. In the 20th century, the script was revived and is again being used. Beginning in 2021, the Government of Manipur began to use the Meitei alongside the Bengali-Assamese script, per the Manipur Official Language (Amendment) Act, 2021.
Since Meitei does not have voiced consonants, there are only fifteen consonant letters used for native words, plus three letters for pure vowels. Nine additional consonants letters inherited from Indic languages are available for writing loan words. There are seven vowel diacritics and a final consonant (/ŋ/) diacritic. The names of the twenty-seven letters are based on parts of the human body.