It is a path either straight or curved, the tangent to which at any point gives the direction of the magnetic field at that point.
Properties of Magnetic Field Lines:
(i) These are always closed loops.
(ii) The lines point from north pole to south pole outside the magnet and from south pole to north pole inside it.
(iii) The magnetic field lines never cross each other. If they do so, then at the point of intersection there will be two tangents which give two directions of magnetic field at the same point which is not possible.
