International Accounting Standard (IAS-26) defines "date of transaction" as the date on which the contract between the parties is accepted, confirmed and acknowledged. "Date of booking" is the date of recording the transaction in the books of A/cs.
Explanation : If the persons / set-ups involved operate in an EDP environment, both the dates can be one and the same. In case of books of accounts manually maintained, the two dates are likely to differ.