The capital Latin letter C is used in mathematics as a variable. For example, it appears in geometric formulas as a variable representing the circumference of a circle. It also is used to represent the set of complex numbers displayed using a “double-struck” typeface.
A variable is a core concept in algebra where a symbol, usualy a lower case latin letter, is used as a placeholder in a math expression.
The circumference of a circle is given the constant τ (tau) multpilied by the radius of the circle, where τ = 2π.
The set of complex numbers contains all possible complex numbers. Each complex number has a real part and an complex part.
The latin letter c is used to represent a variable or coefficient.