Market structure refers to the number of firms that produce a certain type of product. For example, there are two major producers of aircrafts (Boeing and Airbus) and a few smaller ones (like Bombardier) – but there are hundreds of thousands of independent convenience stores in America.

Just as it sounds, an option gives its holder the right (but not the obligation) to conduct a transaction. Options typically exist to buy or sell a stock at a certain price.

The P/E ratio is the value of a company’s stock divided by its annual profit, and it’s used to value companies and compare them against one another.

A private company is privately owned with private shares – investors in a private company can’t buy and sell its shares on a stock exchange like they can with a public company’s.

A private equity firm is an investment firm that invests in the stock of private companies(usually quite large ones) – and/or buys the stock of public companies in order to take them private.

Profit is just revenue minus expenses – in other words, all of the money that a company takes in minus all of the money that it pays out.

A company that is publicly owned, as opposed to a private company. Public companies’ shares are freely traded on stock markets

Quantitative easing is typically put in place when inflation is very low or negative to give the economy a boost. It’s when a central bank, like the US Federal Reserve, directly purchases government bonds from the market (or other, non-government bonds or stocks).

Technically, a recession is when the overall size of an economy shrinks for two consecutive quarters (i.e. its gross domestic product gets smaller). Note that an economy actually shrinking is different than “slowing economic growth”, which is when an economy that’s growing begins to grow at a slower pace (but is still growing).

ROI is essentially how much money is made on an investment in percentage terms. If you invest $100, for example, and end up with $135, your ROI is 35%. It’s typically used to compare different investments, and evaluate how well existing investments are performing.