They are the default catch-all categories. Every new deposit starts in Uncategorized Income and every new withdrawal starts in Uncategorized Expense – both when you add a transaction manually (the modal pre-selects them) and when transactions are imported from your bank. They are system accounts: you cannot rename, deactivate or add accounts to these groups. A transaction sitting in an Uncategorized account cannot be marked as reviewed (Categorize first to mark as reviewed), and on the Profit And Loss Report Uncategorized Income counts as income while Uncategorized Expense counts as an operating expense.