What ≜ means
It marks a definition: “this is defined as that.”
The triangle equals sign, or delta-equal sign, tells you how the author is naming or specifying an expression. In f(x) ≜ x², read it as “f(x) is defined as x squared,” not as a plain statement that two independently established values match.
Unicode also lists “equiangular” as a reading of ≜. That specialized reading fits only when the surrounding notation calls for it.
How did definition signs develop?
They distinguish a definition from ordinary equality.
A related double-equality mark for “equal by definition” is documented in 1920. That earlier notation shows another way to mark definitions; it does not date this exact glyph.
Mathematical authors also use forms such as :, :, and def. They serve related purposes, but the author’s notation guide determines their exact use.
How is ≜ different from :?
Both can introduce a definition; their conventions vary.
Writers commonly use : for a definition or assignment, while ≜ frames the relation as definitional. Neither convention is universal, so follow the paper, textbook, or programming language’s own notation.
Technical; in a formula, it marks an equality introduced as a definition.
Check the writer’s convention before reading it as ordinary equality.
Part of the collection
Don't confuse it with
3
: Colon-equals commonly marks assignment or definition; its exact convention depends on the field.
Related characters
1
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.
More like this
10
How to type or find ≜
- Also called
- triangle equals · triangleq · equal by definition
- Search it as
- defined as · definition symbol · equiangular symbol
- Shows up in
- Anything that takes text · its shape is whatever your font draws
≜\225C\triangleq after loading the amssymb package.≜, ≜, ≜, and ≜.Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.