It represents the sound [ə], the schwa.

[1] As with most special Vietnamese letters, this letter is not well-supported by fonts and is often typed as either o+ or 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, as in phở.

This article related to the Latin script is a stub.