Inductive reactance plane

So I'm learning about electronics and I have a question about coordinates on the Inductive reactance.

They are written as "R+jXl"

R is Resistance, Xl is Inductive Reactance. What is J?

Basicly, since in electrical/electronical equations, you'll use i for current, it would be confusing to use the complex i mathematicians would use for the imaginary unit.