What is meant by the horizontal component of the Earth's magnetic field?I found this horizontal component in a chapter about magnetism. I know it...

The magnetic field lines of the Earth resemble those of a
bar magnet. If we imagine the Earth has a bar magnet pointing to the north and south
poles we can begin to imagine the shape of the field lines in various places. At the
equator they are parallel to the Earths surface or horizontal and the only component is
a horizontal component. At the poles the field lines are vertical - they point straight
down-and there is no horizontal component. At latitudes in between the field lines are
at an angle to the Earths surface. It is possible to represent field lines with VECTORS,
imaginary arrows which show size and direction. Try to imagine a one metre arrow resting
at an angle on the floor. Imagine a shorter vertical arrow sticking up from the same
point on the floor and a shorter horizontal arrow lying on the ground with its tail end
touching the tail ends of the other two. Now imagine that the vertical and horizontal
arrows have lengths that can be added together according to Pythagorus' theorem to equal
the length of the sloping arrow. The horizontal arrow is the HORIZONTAL COMPONENT of the
Earths field at the point.