On Line Transaction Processing.
Anything that you do later, like running a report, is
'off line', and typically 'batch'. Anything that you
do while the data is being created is 'on line'. A
transaction is anything that changes data in the database.
So OLTP means updating the database (and typically
returning a result), in real time, while it actually
happens.
Banks do On Line Processing. Internet sites do On Line
Processing.
A database system may be optimised for OLTP, or On Line
Reporting, or Off Line Reporting, or Batch Transaction
Processing. If your application is small, you may not
care if the database system is optimised for anything.
(david)