The Fed has pumped hundreds of billions into the market through 'repo' offerings. Here's what they are, and why they're back for the first time since the financial crisis.

Repos allow the Federal Reserve to slowly add cash into the economy while watching how markets react. Scheduled repo offerings grant time for policy adjustment, as do the short-term nature of the agreements. Instead of maturing over a span of months or years, these overnight agreements aren't traded and don't see their value fluctuate.

Repo operations were most recently used by the central bank to push interest rates back into their intended range. Short-term rates jumped as high as 10% in the middle of September and threatened to destabilize the bond market. By propping up the money market, the Fed can stabilize interest rates and slowly bring them within the window they feel is best suited for sustainable economic expansion.

September's repo operations were the first from the Fed since the 2008 financial crisis, and marked another government action meant to relieve pressure on nation's economy. The central bank also cut its benchmark interest rate by 25 basis points in September to boost spending.

Here's the Federal Reserve Bank of New York's latest schedule for repo operations through fall 2019, according to the bank's September 20 release.

• September 27: at least $75 billion in overnight repos, and at least $30 billion in 14-day repos
• September 30 to October 10: at least $75 billion in overnight repos

"After October 10, 2019, the Desk will conduct operations as necessary to help maintain the federal funds rate in the target range, the amounts and timing of which have not yet been determined," the bank wrote.

It also clarified that the government assets being offered and subsequently repurchased include Treasury bonds, agency debt, and agency mortgage-backed securities Additional details about each repo offering will be released each afternoon for the following day's operation, according to the Fed.