What ∥ means
It marks a parallel relation.
Ancient mathematicians Heron and Pappus used horizontal double bars around AD 150; the vertical form is documented in Kersey's algebra book in 1673 and mathematician Oughtred's work published in 1677.
Mathematical and technical notation.
What it means when someone sends it to you
2 readingsBetween two line names
The named lines are parallel.
Between resistances
∥ marks a parallel combination; this use became more common in applied electronics around 1974.
Don't confuse it with
2‖
Double Vertical Line
U+2016 DOUBLE VERTICAL LINE is separate; both glyphs use paired vertical strokes.
||
Two ASCII bars are two characters, not the single symbol U+2225.
Questions people ask
1Why does ∥ 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 ∥
Windows (Word)
Alt+XType 2225, then Alt+X to get ∥.
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 “parallel to”.
Linux
Ctrl+Shift+UType 2225, then Enter or Space.
HTML
∥CSS
\2225LaTeX relation
In math mode, type \parallel for relation spacing.
Unicode input
Search the symbol picker for “parallel to.”
Codes and encoding1 code points
HTML decimal
∥
HTML hex
∥
CSS content
content: "\2225";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%88%A5
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.