Question

Define magnatic field?

Answer 1

I would say: a region of space where in every point acts a Magnetic Force.

Explanation:

In a magnetic Field a charged particle `q` moving with a certain velocity `v` will "feel" a force given by:

`vecF=qvecvxxvecB`

where `vecB` represents the Magnetic Field strength.

So you can imagine to be a charge moving in space and suddenly "feel" a force; this "feeling" of perturbation of your motion will tell you that you entered a Magnetic Field.

Hope it helps!