The glyph is a compatibility version of the glyph Glyph for U+03B8Greek Small Letter Theta. 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+03D1 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:
Theta (UK: , US: ; uppercase Θ or ϴ; lowercase θ or ϑ; Ancient Greek: θῆταthē̂ta[tʰɛ̂ːta]; Modern: θήταthī́ta[ˈθita]) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals, it has a value of 9.