Well, I have not heard of this word until today. If you do not know what numismatics means, here is the explanation from WordWeb.
Numismatics means - The collection and study of money (and coins in particular)
We are talking about rare coins that can fetch a lot of money. If you have the money, you can invest in them by buying the coins and store them safely. It is an investment and one that is very lucrative too. Its small, yet valuable. So, you don't have to deal with lands and its fluctuating price. With the low interest rates, saving money also do not make much sense.
So, if it interests you, check out the link and find out more.