This character is a Uppercase Letter and is mainly used in the Greek script. Its lowercase variant is Greek Kai Symbol.
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. The word that U+03CF forms with similar adjacent characters prevents a line break inside it.
The Wikipedia has the following information about this codepoint:
Kai (και "and"; Modern Greek:[ce]; Ancient Greek:[kai]; sometimes abbreviated k) is a word that is a conjunction in Greek, Coptic (ⲕⲁⲓ) and Esperanto (kaj; IPA:[kai̯]).
Kai is the most frequent word in any Greek text and thus used by statisticians to assess authorship of ancient manuscripts based on the number of times it is used.
Representations
System
Representation (click value to copy)
Nº
975
UTF-8
CF 8F
UTF-16
03 CF
UTF-32
00 00 03 CF
URL-Quoted
%CF%8F
HTML hex reference
Ϗ
Wrong windows-1252 Mojibake
Ï
Encoding: GB18030 (hex bytes)
81 30 CC 35
RFC 5137
\u'03CF'
Bash and Zsh inside echo -e
\u03CF
C and C++
\u03CF
C#
\u03CF
CSS
\0003CF
Excel
=UNICHAR(975)
Go
\u03CF
JavaScript
\u03CF
Modern JavaScript since ES6
\u{3cf}
JSON
\u03CF
Java
\u03CF
Lua
\u{3CF}
Matlab
char(975)
Perl
"\x{3CF}"
PHP
\u{3cf}
PostgreSQL
U&'\03CF'
PowerShell
`u{3CF}
Python
\u03CF
Ruby
\u{3cf}
Rust
\u{3cf}
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