It is omega, and looks a little like w.
In physics, omega stands for angular velocity.
w = dθ /dt where θ is angular displacement and t is time.
In many electricity/magnetism formulae, 2*pi*w is found.
The unit of angular velocity is radians and 2*pi radians is equal to 360 degrees.
Interestingly, alpha is angular acceleration, dw/dt or d²θ /dt².
The Greek alphabets are used to represent various parameters in Physics, like mu is refractive index, rho is specific gravity (and specific resistance too), lambda is wavelenght etc.