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+25AC forms with similar adjacent characters prevents a line break inside it.
The CLDR project calls this character “filled rectangle” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: filled, rectangle.
The Wikipedia has the following information about this codepoint:
Geometric Shapes is a Unicode block of 96 symbols at code point range U+25A0–25FF.
Representations
System
Representation (click value to copy)
Nº
9644
UTF-8
E2 96 AC
UTF-16
25 AC
UTF-32
00 00 25 AC
URL-Quoted
%E2%96%AC
HTML hex reference
▬
Wrong windows-1252 Mojibake
â–¬
Encoding: GB18030 (hex bytes)
81 37 9B 36
Adobe Glyph List
blackrectangle
Adobe Glyph List
filledrect
digraph
SR
RFC 5137
\u'25AC'
Bash and Zsh inside echo -e
\u25AC
C and C++
\u25AC
C#
\u25AC
CSS
\0025AC
Excel
=UNICHAR(9644)
Go
\u25AC
JavaScript
\u25AC
Modern JavaScript since ES6
\u{25ac}
JSON
\u25AC
Java
\u25AC
Lua
\u{25AC}
Matlab
char(9644)
Perl
"\x{25AC}"
PHP
\u{25ac}
PostgreSQL
U&'\25AC'
PowerShell
`u{25AC}
Python
\u25AC
Ruby
\u{25ac}
Rust
\u{25ac}
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