What is the primary application used to load data into ServiceNow?

Service Level Management is an application for defining, monitoring, and reporting on service level agreements, not for importing raw data.

Configuration refers to various system settings and customization, but it is not a specific application for loading data.

System Import Sets is the core ServiceNow application designed to facilitate the import of data from various external sources (like spreadsheets, JDBC, web services) into staging tables, where it can then be transformed and mapped to target tables.

System Update Sets are used to move customizations and configuration changes between ServiceNow instances, not to import transactional or master data from external sources.