ANSWER

OLTP or On-Line Transaction Processing systems are a class of systems which contain current, operational data used to control and run fundamental business tasks.  OLTP systems are typically characterized by their ability to complete many concurrent database transactions and are designed for optimal database transaction speed. Additions and changes to data are user initiated (rather than scheduled) and conducted via short, atomic transactions.

Queries of OLTP systems are typically simple and return relatively few records.  The structure of OLTP databases are highly normalized which means tables and fields are organized to minimize data redundancy and dependency.  But this doesn’t lend itself to efficient processing of complex queries. More complex querying is typically run against historical data stores which are classified as OLAP systems (On-Line Analytical Processing) or Data Warehouses.

Transaction and data recovery is paramount for OLTP systems since they deal with current business data used to conduct real-time business operations. Similarly, OLTP systems are often decentralized to avoid single points of failure.  This can also help spread volume over multiple servers to maximum the volume transaction processing possible and minimize response times.