Online Transaction Processing - database systems optimized for handling many small transactions quickly. Like a busy cash register that processes hundreds of purchases efficiently.
E-commerce websites use OLTP databases to handle thousands of order transactions per minute.
OLTP is a workload pattern (many short, concurrent reads/writes with strict consistency). These managed relational databases are commonly used to run OLTP applications; they differ in engine options, scaling methods, and operational features, but all support transactional ACID behavior.