This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+259D 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:
Block Elements is a Unicode block containing square block symbols of various fill and shading. Used along with block elements are box-drawing characters, shade characters, and terminal graphic characters. These can be used for filling regions of the screen and portraying drop shadows. Its block name in Unicode 1.0 was Blocks.
Representations
System
Representation (click value to copy)
Nº
9629
UTF-8
E2 96 9D
UTF-16
25 9D
UTF-32
00 00 25 9D
URL-Quoted
%E2%96%9D
HTML hex reference
▝
Wrong windows-1252 Mojibake
â–
Encoding: GB18030 (hex bytes)
81 37 9A 33
RFC 5137
\u'259D'
Bash and Zsh inside echo -e
\u259D
C and C++
\u259D
C#
\u259D
CSS
\00259D
Excel
=UNICHAR(9629)
Go
\u259D
JavaScript
\u259D
Modern JavaScript since ES6
\u{259d}
JSON
\u259D
Java
\u259D
Lua
\u{259D}
Matlab
char(9629)
Perl
"\x{259D}"
PHP
\u{259d}
PostgreSQL
U&'\259D'
PowerShell
`u{259D}
Python
\u259D
Ruby
\u{259d}
Rust
\u{259d}
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