Language is communication of information.

Money is that which satisfies the condition in a conditional exchange of information. Everything is information.

I will give you this is you give me "that". Money is that.

That can be labour, knowledge, goods, service, etc.

The best money is the most sellable good. The best thing to have as the most sellable good is something scarce as in hard to produce. Unless you're a selfish actor.

An even better money from a selfish viewpoint would be.

The most sellable good.

Something that is scarce to everyone except me.

Governments have really nailed the latter. The most pure form of sin money possible.