1. A remedy for a social, political, or economic problem; especially, an idea or plan that is often suggested but never proven to be successful; a favorite but untested remedy for problems or evils.
2. A medicine prepared or prescribed by an unqualified person whose claims for its effectiveness have no scientific or proven basis and the ingredients of which are usually secret; a quack remedy.
Quacks is a term for people who boast and pretend to cure diseases and the quack medicines they use for the treatment of diseases or the effects to be achieved with such treatments.
The historical basis for this "nostrum" word
The Great Plague of 1665-66 saw a great influx of quacks from Holland, charlatans from France, and mountebanks from Italy going around claiming to have "secret cures".
All of these people proclaimed the virtues of the secret concoction that they alone could produce. So, to make their claims more impressive, they labeled their "cures" as Nostrum, perhaps to impress people with their knowledge of Latin.
The term became a general name for any quack medicine or, in later years, for a patent medicine; however, the Latin meaning of nostrum, is merely "Our own"; that is, "our own remedy preparation".