  Magnetic winding is a fundamental topological quantity that underpins
magnetic helicity and measures the entanglement of magnetic field lines. Like
magnetic helicity, magnetic winding is also an invariant of ideal
magnetohydrodynamics. In this article we give a detailed description of what
magnetic winding describes, how to calculate it and how to interpret it in
relation to helicity. We show how magnetic winding provides a clear topological
description of magnetic fields (open or closed) and we give examples to show
how magnetic winding and helicity can behave differently, thus revealing
different and imporant information about the underlying magnetic field.
