OLTP stands for Online Transaction Processing system & OLAP stands for Online Analytical processing system. OLTP maintains the transactional data of the business & is highly normalized generally. On the contrary, OLAP is for analysis and reporting purpose & it is in de-normalized form.

This difference between OLAP and OLTP also gives you the way to choosing the design of schema. If your system is OLTP, you should go with star schema design and if your system is OLAP, you should go with snowflake schema.