The basic principle of double entry bookkeeping is that every transaction has a twofold effect. In other words, a value is received and a value is yielded or parted with. Both effects, which are equal in amount, must be entered completely in the bookkeeping records.
  According to this principle, all transaction affect at least two accounts. Each transaction must be analyzed to determine which accounts are affected, and whether they should be increased or decreased. An entry made on the left hand side or column of an account is called a debit, while an entry made on the right hand side or column is called a credit. Debit, usually abbreviated DR, at one time meant value received, or literally he owes. Credit, usually abbreviated CR, meant value parted with, or literally he trusts, in modern bookkeeping, debit refers only to the left-hand side of account, whereas credit refers to the right-hand side. Some bookkeepers use a far right-hand column to keep an up-to-date balance of the account.
  In double-entry bookkeeping, a book in which both the debit side and the credit side of the transaction are entered is called a journal, while another book used to list all the accounts of an organization is called a ledger. Entries from the journal are transferred to the ledger at regular intervals, usually monthly. This process is called posting.