The glyph is not a composition. Its width in East Asian texts is determined by its context. It can be displayed wide or narrow. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+03A9 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with 9 other glyphs.
The Wikipedia has the following information about this codepoint:
Omega (US: , UK: ; uppercase Ω, lowercase ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and last letter in the Greek alphabet. In the Greek numeric system/isopsephy (gematria), it has a value of 800. The word literally means "great O" (ō mega, mega meaning "great"), as opposed to omicron, which means "little O" (o mikron, micron meaning "little").
In phonetic terms, the Ancient Greek Ω represented a long open-mid back rounded vowel IPA:[ɔː], comparable to the "aw" of the English word raw in dialects without the cot–caught merger, in contrast to omicron which represented the close-mid back rounded vowel IPA:[o] , and the digraph ου which represented the long close-mid back rounded vowel IPA:[oː]. In Modern Greek, both omega and omicron represent the mid back rounded vowel IPA:[o̞] or IPA:[ɔ̝]. The letter omega is transliterated into a Latin-script alphabet as ō or simply o.
As the final letter in the Greek alphabet, omega is often used to denote the last, the end, or the ultimate limit of a set, in contrast to alpha, the first letter of the Greek alphabet; see Alpha and Omega.