What is Jesus referring to as trading in the parable of the talents.

First of all, what is a “talent”? The English Standard Version Study Bible notes say that in Old Testament times a talent was a unit of weight equalling about 75 pounds (34 kg.).

In New Testament times, it [a talent] was a unit of monetary reckoning (though not an actual coin), valued at about 6,000 drachmas, the equivalent of about 20 years’ wages for a labourer.

In the parable of the talents, the master of the house is clearly entrusting money to his servants. The New Living Translation says the master of the house “gave five bags of silver to one, two bags of silver to another, and one bag of silver to the last” (Matthew 25:15). If each bag (or talent) weighed 75 pounds (34 kg.) and contained silver coinage, then the value of each talent would have been considerable.

When used as a measure of money, it refers to a talent-weight of gold or of silver. In June, 2018, the international price of gold was about US$41,155.69 per kilogram. One gram costs about $38. At this price, a talent (33 kg) would be worth about $1,400,116.57. Similarly, in February 2016, the price of silver was about $15 per troy ounce or about 50 cents per gram, so a 33 kg silver talent would be worth about $16,500... The talent as a unit of coinage is mentioned in the New Testament in Jesus' parable of the talents. One talent was an incredible amount of money. Source: https://simple.wikipedia.org/wiki/Talent_(weight)

Whatever each talent was worth, the master of the house, who was going away on a journey of indeterminate time, expected his servants to put this money to good use. Upon his return, the servant who took his single talent and buried it in the ground was severely reprimanded by his master:

“You should have put my money on deposit with the bankers, so that when I returned I would have received it back with interest.” (Matthew 25:27, New International Version)

The Greek word for bankers comes from trapeza (table), a word seen on the front of banks in Greece today. Bankers sat at small tables and changed money. (Source: New International Version Study Bible notes on Matthew 25:27) The English Standard Version Study Bible notes makes this comment regarding Matthew 25:27:

“In the O.T. Israelites were forbidden from charging interest to other Israelites, but it was permissible to charge interest on money loaned to Gentiles (Deut. 23:20).”

This is confirmed in this Wiki article on banking: https://en.wikipedia.org/wiki/History_of_banking#Judaism

The same Wiki article comments that “in ancient Greece and during the Roman Empire, lenders based in temples made loans, while accepting deposits and performing the change of money.” https://en.wikipedia.org/wiki/History_of_banking

It would therefore seem likely that the master of the house expected his servants to put his money to work by depositing it with the bankers so that it would earn interest while the master was away.

A "talent" in this passage refers to a large amount of money.

Being money, it was probably traded in the finance and investment sector, used to pay wages, or used for purchasing goods in the market. But, it is not a single denomination of currency, it is an amount of money.

To be very, very slang—yet also make the point to the audience—one could VERY loosely translate it as "a suitcase of money". What can you trade with a "suitcase of money"?—a lot! (Of course, a 'talent' is more specific than just a 'bag full' or a 'suitcase full', but it was probably delivered in a bag, or something similar, since it was so much money.)

Consider this Wikipedia article...

Assuming it was the "Attic talent", one talent would have been worth about nine years of manual labor. If the "Homeric talent", it would have been only worth an ox. Most Bible teachers would lean toward the larger amount. But, either way, it was worth a substantial amount of money.

The term "talent" as a kind of natural knack for gaining a skill is not what is meant here. Some argue that using the word "talent" to refer to a skill aptitude was an application from this passage, but that would have been after the fact, applying the Bible figuratively. It is not unusual for the Bible to influence language.

Usury (ie: charging interest) was forbidden among Jews but it was permitted, or possibly required for Jews to charge interest when lending to gentiles.

However this is not a loan situation, per se but rather a situation where a man's slave was being employed as his money manager (οἰκονόμος). He neither would lend nor give the money to his slave but instead committed it to him for his (the master's) purposes:

1Co 4:1-2 KJV - 1 Let a man so account of us, as of the ministers [IE: "servants"] of Christ, and stewards (οἰκονόμοις) of the mysteries of God. 2 Moreover it is required in stewards that a man be found faithful.

Of course, while there is application regarding "filthy lucre" the intent of the parable is really about redeeming the time.

To "redeem" time is to leverage time for profit. Again, a very capitalist idea. Paul is saying that time spent without profit is "un-redeemed". Paul is saying to "do not waste your time but rather invest it" by putting your gifts to work in serving others:

1Pe 4:10 NIV Each of you should use whatever gift you have received to serve others, as faithful stewards of God’s grace in its various forms.

It was his duty to put the money to work to gain more money. This is essentially the capitalist paradigm. People invest in a corporation for entirely selfish ends. The corporation then uses the money to make more money and return a dividend to the investor. If the corporation does not create more wealth for the investor then the investor takes the money he invested and invests it into a different corporation. And so on. This is a ruthless, greed driven enterprise, and in no way a charity.

The slave that buried the money blames his failure to profit on his master. Fear of his master's ruthless craving for profit motivates the servant to hide the money. However, the master is not pleased because he has no profit and correctly points out that he could have made a profit with no risk (or at least without taking a risk for which he would have been censured if the bank failed). Banks take money from risk averse investors and then turn around and invest it in riskier ventures at higher profit. Then they pay out at a lower rate.

Now, the slaves that returned a high profit to their master evidently took calculated risks by researching the market well and making informed investments. The risks reaped large rewards. The master took his investment from the one who was both risk averse and delinquent and invested it with the servant who took the greatest risk and reaped the greatest reward. The capitalist master wanted to hit it big on the latest dot com, not just get a 1% bank interest.

The reward to the master was only on paper. His money remained in the market. The reward to the profitable servant was not in money (since neither the seed money nor the profit belonged to him) but in the approval of his master and the ever increasing responsibility.

What is absent from the parable is a slave who took risk and lost the seed money. One can only speculate how the master might react which would depend on his character.

So what the slave was saying is this:

"[The reason I didn't make any profit for you is that I knew that] you are very demanding, expecting your money to bring you profits you didn't work for. [So I didn't take any chances and I protected your investment]".

The master responded "You knew I demanded a profit I didn't work for [which isn't an impossible demand in that] you could have at least put my money in the bank and I would have gotten my seed money back with interest. ["So the fault is not mine for demanding a return I didn't work for but yours for being too lazy and irresponsible to invest the money I entrusted to your management into a bank."]

God wants profitable servants, not excuses. And God's servants are given risk-free opportunities for investment. The bank here seems to be connected with the following section and so means that the lord's servant should, with the resources he has been entrusted, invest in the poor. Money invested in the poor is like money in the bank. At the lord's coming he will be found a faithful and gratifying servant to his master.