Curiosity doesn't kill the fox. It empowers it!
“Imported Accounts” are referenced as “Loose Accounts” in previous MetaMask versions [versions before 4.1.3 Beta UI]. Imported Accounts are accounts you import. These accounts will not appear automatically when you restore your MetaMask account with your seed phrase. The data associated with your seed phrase cannot be added or extended to new Ethereum addresses imported.
Therefore, it is important that you keep the information you use to access Imported Accounts separately somewhere safe to recover these accounts. (Similar to how you should keep your seed phrase backed up offline).
Imported Accounts are shown on the MetaMask interface. You may see this tag by:
i) Clicking on the icon at the upper right corner next to the network indicator tag to open the dropdown menu.
ii) Click on the bars on the upper left corner below the Fox