OLAP [Online analytical processing] is a computer technology term referring to systems focused on analysing data in a specific database.The standard applications  are bussiness intelligence and reporting.There are many types systems. The most common are: MOLAP, ROLAP and HOLAP.

OLTP [Online Transaction Processing] is a information system type that prioritizes transaction processing, dealing with operational data.The main applications are all kind of transactional systems like databases, hospital applications.. All client-server architectures are based on these processes.

OLTP-Online Transcation Processing.
OLAP-Online Analytical Processing.

OLTP-application is Management, operational, web services, client-server.
OLAP-application is 
Management Systems. Reporting, decision.

OLTP-data model is 
Entity-relantionship on databases.
OLAP-data model is
One or multi-dimensional data.