OLTP (online transaction processing) is a class of software programs capable of supporting transaction-oriented applications on the Internet.
Typically, OLTP systems are used for order entry, financial transactions, customer relationship management (CRM) and retail sales. Such systems have a large number of users who conduct short transactions. Database queries are usually simple, require sub-second response times and return relatively few records.
An important attribute of an OLTP system is its ability to maintain concurrency. To avoid single points of failure, OLTP systems are often decentralized.
IBM's CICS (Customer Information Control System) is a well-known OLTP product.
Learn how SQL Server 2014 leverages in-memory OLTP technology