If you see the following pop-up in MetaMask:
That means that you are unable to connect with the host running the blockchain node that your MetaMask wallet is configured to connect to for purposes of reading the blockchain and executing transactions.
For the convenience of MetaMask users, the blockchain node service Infura is configured as the default blockchain host. Any loss of connection would likely be temporary due to a technical issue.
But like many features in MetaMask, which blockchain host the wallet connects to is customizable, meaning you can change it to connect to any other blockchain node, whether offered by a service or one that you run yourself. While the Infura service is industry leading for many important reasons (reliable up-time, ease of use), users may choose to have a backup service on standby should there be any service disruptions.