OLAP and OLTP can be easily confused. A quick summary of the differences
OLTP: Online Transaction Processing; enables real-time execution of large numbers of database transactions typically updating data in multiple tables with foreign keys and providing transactional guarantees and rollbacks.
OLAP: Online Analytical Processing; system to enable multi-dimensional analysis of large volumes of data typically for reporting purposes. Backing data is typically some sort of data warehouse but can also be an OLTP data store.
OLAP databases are typically columnar.