A ledger is a book containing accounts that records all business transactions. It allows the transfer of transactions from journals into separate accounts. The document discusses key aspects of ledgers including components like date, amount, particulars; examples of common ledger accounts; the T-format used; and the process of posting journal entries to ledger accounts. It also covers the meaning of debit and credit balances, preparation of trial balances to check the accuracy of accounts, and common types of accounting errors.