What ㌹ means
It represents ヘルツ, the Japanese word for hertz.
Katakana is the Japanese syllabic script; ヘルツ spells the frequency unit in three characters. This compatibility character packs those kana into one square cell, a format carried over from older Japanese encodings. The arrangement may differ between horizontal and vertical text, while the reading stays the same.
It is a compact form from Japanese unit typography; ヘルツ or Hz reads more plainly in ordinary technical text.
Don't confuse it with
2ヘルツ
Is it the same unit? Yes: this is the ordinary three-kana spelling, not the packed one-character form.
Hz
The standard Latin-letter symbol for hertz; it names the same unit in different notation.
Questions people ask
1Why does ㌹ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ㌹
Windows (Word)
Alt+XType 3339, then Alt+X to get ㌹.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “square herutu”.
Linux
Ctrl+Shift+UType 3339, then Enter or Space.
HTML
㌹CSS
\3339Codes and encoding1 code points
HTML decimal
㌹
HTML hex
㌹
CSS content
content: "\3339";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E3%8C%B9
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.