It is a real function of a real variable.
A real function is defined through menu item Calculus - New real calculation - Real function.
The calculus may be modified afterwards with tool .
For example, to define a function with formula f(x) = sin(2x) enter f as name, x as formal variable and enter sin(2*x) for formula but you can also choose t as formal variable and enter sin(2*t) for formula.
See also : Real calculus syntax.