Based on this page, I know it means STOP but i can't figure out what they would STOP.
Raising that target to 3 or even 4 percent as some economists have suggested would shift the outlook of firms in particular, allowing them to charge more for goods and pay more for labor without the fear that a central bank would step on the brakes."
The US Federal Reserve (FED) is mandated to maintain inflation within a targeted band. As economic activity increases, the risk of inflation also increases. By slowing down the economy, the risk of inflation abates.
One way the FED slows down the economy is by raising interest rates (stepping on the brakes).
What the article is saying is, if the FED's policy targets a high enough interest rate which already accommodates economic growth, businesses would not have to worry about the FED raising rates further (stepping on the brakes) to slow the economy down.
This is important since businesses want certainty so they can plan for the future.
You can think of it in that context to mean the bank would slow them down or stop that from occuring
Edit: Them being the party or person the bank is slowing down
That being the action (s) being performed by the party or person in question that the bank we will be attempting to slow down or stop
This expression doesn't only mean stop, it can also mean slow down (just like you can use brakes in a car to stop or to slow down).
You provided a link to a dictionary that only mentions stopping – and I've upvoted your question for showing your research. However, it's often good to check more than one dictionary, as sometimes a dictionary won't quite capture all the possible usages of a word.
In this case, we can find more at Cambridge, which says:
put the brakes on to slow down or stop an activity : The city has put the brakes on further spending.
or at Collins, which says:
brake (noun) You can use brake in a number of expressions to indicate that something has slowed down or stopped : Illness had put a brake on his progress.
The expressions hit the breaks and put the brakes on are pretty much interchangeable when it comes to these metaphorical usages.
'Step on the brakes' means to stop as quickly as possible. It comes from the days when Cars and Lorries did not have power operated brakes and to stop quickly you needed to put a lot of pressure on the brake peddle hence you put your full weight on the peddle and raised yourself out of your seat.
