From Wikipedia:
Numismatics (Latin: numisma, nomisma, "coin"; from the Greek: νομίζειν nomízein, "to use according to law") is the scientific study of currency and its history in all its varied forms. While numismatists are often characterized as students or collectors of coins, the discipline also includes a much larger study of payment media used to resolve debts and the exchange of goods.
Indonesian translation:
Numismatik (Latin: numisma, nomisma, "koin"; from the Greek: νομίζειν nomízein, "digunakan sesuai aturan") adalah bidang studi mengenai alat tukar (uang) dan sejarahnya dalam segala bentuk. Walau numismatis biasanya dicirikan oleh orang yang mempelajari uang atau orang yang mengkoleksi uang, bidang studi ini juga mempelakari mengenai alat-alat tukar lain yang dipakai untuk membayar hutang dan membeli barang.
Again, even though it's cool to call yourself "numismatist (numismatis)", it's not the correct term to use for coin/money collection. Just like calling yourself philatelist (filatelis) just because you're collecting stamps.