http://www.investopedia.com/terms/j/journal.asp

Definition of 'Journal'
1. In accounting, a first recording of financial transactions as they occur in time, so that they can then be used for future reconciling and transfer to other official accounting records such as the general ledger. A journal will state the date of the transaction, which account(s) were affected and the amounts, usually in a double-entry bookkeeping method.

2. For an individual investor or professional manager, a detailed record of trades occurring in the investor's own accounts, used for tax, evaluation and auditing purposes.

 
 Investopedia explains 'Journal'
Journaling is an essential part of objective record-keeping and allows for concise review and records transfer later in the accounting process. Journals are often reviewed as part of a trade or audit process, along with the general ledger(s).

 
Definition of 'General Ledger'
A company's main accounting records. A general ledger is a complete record of financial transactions over the life of a company. The ledger holds account information that is needed to prepare financial statements, and includes accounts for assets, liabilities, owners' equity, revenues and expenses.

A general ledger is typically used by businesses that employ the double-entry bookkeeping method - where each financial transaction is posted twice, as both a debit and a credit, and where each account has two columns. Because a debit in one account is offset by a credit in a different account, the sum of all debits will be equal to the sum of all credits. 
 Investopedia explains 'General Ledger'
A company's general ledger can either be a physical book into which credits and debits are posted, or an accounting computer program where the various credits and debits are entered. The general ledger's double-entry bookkeeping requires that each transaction will be entered on the left side, or debit side, of one account and simultaneously on the right side, or credit side, of another account. A general ledger is used to prepare financial statements directly from the accounts, and as a means to identify errors and/or instances of fraud. 

Definition of 'Double Entry'
The fundamental concept underlying present-day bookkeeping and accounting. Double entry accounting is based on the fact that every financial transaction has equal and opposite effects in at least two different accounts. It is used to satisfy the equation Assets = Liabilities + Equity, whereby each entry is recorded so as to maintain the relationship. 
 Investopedia explains 'Double Entry'
In the double entry system, transactions are recorded in terms of debits and credits. Since a debit in one account will be offset by a credit in another account, the sum of all debits must therefore be exactly equal to the sum of all credits. The double-entry system of bookkeeping or accounting makes it easier to accurately prepare financial statements directly from the books of account and detect errors.