Geometry triangle symbol.
The capital greek letter Δ (Delta) is used in mathematics to represent the change in a variable.
The upside down triangle is an alternative to the nable symbol to represent a gradient.
A triangle is a three sided geometric shape. The shape forms a basis for the subject of trigonometry and is used throughout mathematics and programming.
A triangle is denoted using the triangle symbol followed by three letters that represent the points of the triangle.