The website of the Central Bank of Brazil (BCB) states its mission (in Portuguese; my translation):
"To ensure the stability of the currency's purchasing power and a sound and efficient financial system"
In other words, the BCB is saying that its mission is to control inflation. How does it do that? One of the main tools is the country's interest rate. This rate signals the cost of money. In a hypothetical transaction with no credit risk, it is what people have to pay to borrow money. On the other side, if you have spare cash to invest, it is what you would earn on a risk-free investment.
So what does this have to do with inflation?
In very simple terms, picture a business owner who wants to buy a machine to expand a factory's production capacity. With money saved, the owner has to withdraw that investment to buy the machine. Without it, the owner can go to the bank and ask for a loan.
In both cases, the higher the interest rate, the less likely the machine gets bought. If the money is invested, it may earn more at the bank than it would from buying the machine and producing. If the owner needs the loan, the interest may wipe out the profit the machine would have generated.
We know that the more people consume, buy and invest in the real economy, the hotter the economy runs, and that ends up pushing inflation up. So by controlling the interest rate, the Central Bank has a very powerful tool to control inflation. Of course, the example above is very simple and by no means exhaustive. Many other factors and tools affect inflation. But for our purposes, it is more than enough.
Selic
All of that was a long way of explaining that every 45 days the Central Bank reviews the Selic target, Brazil's base interest rate, to decide whether it needs to change it in pursuit of the year's inflation target. In technical terms, this rate is called the Selic Meta (Selic target), because it is the rate the Central Bank aims for.
Remember my post on the CDI, the Brazilian interbank deposit rate? Besides settling their cash positions with each other, banks also lend to and borrow from the Central Bank. When they do, the transaction is registered in the Sistema Especial de Liquidação e Custódia (Special System for Settlement and Custody), known as SELIC.
If you read the CDI post, you have already figured it out. SELIC publishes the daily average rate of the transactions it registers. This rate is called the Selic Referencial (Selic reference rate). It is also the rate applied to one of the bonds issued by Brazil's National Treasury, the LFT, sold to retail investors as Tesouro Selic. In financial markets, everything is connected. Curious? A post on that is coming soon.
Copom
Copom is the committee that meets every 45 days. It is made up of the Central Bank's directors, and the name stands for Comitê de Política Monetária, the monetary policy committee.