an area of interest or activity in English:

We will slowly move from the realm of theory into the sphere of practice.

Even a million Dothraki are no threat to the realm, as long as they remain on the other side of the Narrow Sea.

interests are in the realm of practical politics.

This year, there have been many new discoveries in the realm of science.

You should stick to the realm of politics; that is your area of expertise after all.

What these acts said was that it was illegal to pay someone in anything other than coin of the realm.

Public opinion plays a vital in the political realm.

Instead of giving the money, that is the normal coin of the realm, which is the phrase that everyone used then, they would give them a token, and this token might be metal, might be wood, might be cardboard.