@esxokm welcome to the METAR Board. Your question is absolutely on-topic.
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@DrBob2 gave you an excellent answer. Please let me add to it.
MBS are “Mortgage-Backed Securities.” A mortgage is a debt and therefore falls into the broad category of bonds.
Mortgage originators (lenders) carry some risk because the borrower may default. In order to diffuse the risk the originator often sells the mortgage to a brokerage.
The originator gets cash which it can lend out for more mortgages.
The brokerage “bundles” the specific mortgage with many other mortgages. The bundle of mortgages generates a bundled cash flow. The brokerage evaluates the credit ratings of each mortgage holder in the bundle and then “slices” the bundle into “tranches” of similar credit ratings.
These tranches of debt are put on the market for investors to buy to get income. They are called “mortgage backed securities” or MBS. They are derivatives because they have been massaged, sliced and diced and aren’t the original security (which was a collection of simple mortgages). The bundles are then sold to investors.
The roots of the Great Financial Crisis of 2008 were in 1. many unqualified borrowers being loaned mortgages for houses they couldn’t afford and 2. many MBS being created with credit ratings that investors trusted but were stronger than they deserved.
Like all investments, bond prices (and the MBS that contain mortgage bonds) respond to supply and demand. If there is more demand the price will go up. With bonds, the interest rate goes up when the price goes down. The interest rate goes down when the price goes up.
The Federal Reserve bought a huge amount of MBS with money it created out of thin air. @DrBob2 showed the chart. By increasing the demand for MBS the Fed pushed the price up and so the interest rate went down. This fed into the marketplace where the mortgage rate went down.
Now the Fed is “rolling off” its MBS. That mean that the Fed will not buy new bonds when the old bonds mature. You can see this in the line that is sloping down.
The Fed provided a huge demand for MBS which isn’t there anymore. With less demand the price of MBS is going down. That means the yield is going up.
MBS are mortgage-backed securities. As the yield goes up the increase is passed along to individuals who want mortgages to buy a home.
You can see from this chart how the 30-Year Fixed Rate Mortgage Average in the United States rose at the same time that the Fed’s investment in MBS fell.
That is the exact meaning of the sentence you asked about.
Wendy