As we have learned, Jewish law does not recognize the validity of a kinyan – a purchase – made with money, unless the buyer also takes possession of the object that he purchased. Furthermore we saw that this applies to purchases made with money, but that when trading one object for another, as soon as a kinyan is made on the first thing, the trade takes effect.
In defining the term asimon, the Gemara on today’s daf quotes Rav as saying that it is a token that is used in the bathhouse. It was common practice for bathhouses to distribute metal “entrance tickets” that were later used to collect payment. The Gemara rejects this understanding of asimon because of a Mishna where we find that there is a difference of opinion as to whether an asimon can be used to redeem ma’aser sheni (the tithe taken to Jerusalem), but all agree that a bathhouse token cannot be used. The Gemara accepts the opinion quoted in the name of Rabbi Yohanan, that an asimon is a pulsa – a metal piece that is empty of any form.
Rashi explains that the asimon has no form on it because it has not yet been stamped, but many of the rishonim suggest that it once had a design stamped on it, but it became rubbed off and can no longer be used as a coin or it was stamped with something other than normal coinage. According to the Meiri it is a coin that was stamped in a negative fashion, i.e. rather than standing out, the form on the coin is indented.