The glyph is a canonical composition of the glyphs Glyph for U+004FLatin Capital Letter O, Glyph for U+031BCombining Horn. 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. The word that U+01A0 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with one other glyph.
The Wikipedia has the following information about this codepoint:
Ơ (lowercase ơ) is one of the 12 Vietnamese language vowels. It is pronounced [ə].
As with most special Vietnamese letters, this letter is not well-supported by fonts and is often typed as either o+ or o*. The VIQR standard is o+.
On the Windows default Vietnamese keyboard Ơ can be found on where the ] key is on a US English keyboard layout.
Because Vietnamese is a tonal language this letter may optionally have any one of the five tonal symbols above or below it.