Very much like it sounds, bulk loading is a process whereby one can load large amounts of data into a database in a relatively short period of time.
Database indexes are typically optimized for inserting rows one at a time. However, when you need to load a lot of data all at once, inserting rows of data one at a time is often very slow and inefficient.
Bulk loading is used when you need to import or export large amounts of data relatively quickly. With bulk loading operations, you don’t just insert data one row at a time; data is instead inserted through a variety of more efficient methods based on the structure of the specific database.
Bulk loading operations are typically not logged and transactional integrity can therefore be an issue. Bulk operations also frequently bypass triggers and integrity checks such as constraints. Bypassing these slow processes can significantly improve data loading performance, resulting in the operation taking much less time than loading data by rows.
Bulk loading is also called bulk insert for SQL Server databases.