We are all familiar with magnetic fields, or at least with magnets.
Magnets always come with pairs of opposing poles, identified as north and south .
This differs in an important way from electric charges which do not have to come in opposing pairs. Like poles will repel each other while unlike poles will attract. Historical note the north pole of a magnet is that end which will point north when allowed to swing freely. We know a magnetic field is present in space if a small test magnet, such as a compass, feels a torque tending to line it up in a particular direction. Whip out your pocket compass and see which way it points that is the direction of the local magnetic field.