δ
Symbol  Format  Data 

δ  Code Point 
U+03B4 
TeX 
\delta 

SVG 
The (delta) symbol is used in math as a variable. In calculus, the symbol used in epsilondelta notation when defining the limit operator^{[1]}.
The capital Greek letter Δ (Delta) is used in mathematics to represent the change in a variable.

(ε, δ) "epsilon delta" definitions of limitsGrant Sanderson (3Blue1Brown)