What are offline logs on FortiAnalyzer?

[Reference:https://help.fortinet.com/fa/faz50hlp/56/5-6-6/Content/FortiAnalyzer_Admin_Guide/0300_Key_concepts/0600_Log_Storage/0400_Archive_analytics_logs.htm, Logs are received and saved in a log file on the FortiAnalyzer disks. Eventually, when the log file reaches a configured size, or at a set schedule, it is rolled over by being renamed. These files (rolled or otherwise) are known as archive logs and are considered offline so they don’t offer immediate analytic support. Combined, they count toward the archive quota and retention limits, and they are deleted based on the ADOM data policy. FortiAnalyzer_7.0_Study_Guide-Online page 140, ]