A balance sheet account is any asset, liability or owner's equity account in the general ledger. These are the same accounts that accountants call permanent accounts or real accounts, because their balances are not closed at year end but carry forward into the next period. They take their name from the statement they feed, the balance sheet.
How they differ from income statement accounts
A ledger contains two broad groups of accounts. Balance sheet accounts record what a business owns and owes at a point in time: Cash, Accounts Receivable, Inventory, Equipment, Accounts Payable, Notes Payable, Common Stock and Retained Earnings are typical examples. Income statement accounts, also called temporary accounts, record revenues, expenses, gains and losses for a period of time.
At the end of each year, temporary accounts are closed to zero, usually through the income summary account, and their net result is transferred to retained earnings. Balance sheet accounts are not closed. The December 31 balance of Cash, for example, becomes the January 1 opening balance.
The owner's drawing account in a sole proprietorship and dividends declared in a corporation are exceptions in practice: they relate to equity but are closed at year end like temporary accounts. Contra accounts such as accumulated depreciation are balance sheet accounts and carry forward.