Question

What does the crowding of field lines mean?

Answer 1

the field lines is just a hypothetical represent ation of strength and direction of force cause by magnetic field

Answer 2

Field lines are just hypothetical representation of the strength of field and direction of force (on N pole in case of magnetic field and on positive charge in case of electric field) at any particular point.

So, crowded lines represent strong field i.e. higher field strength and distant lines represent the weak field.