@Ladsgroup and @GoranSMilovanovic will develop a concise documentation page going into some more detail on usage aspects in the Wikibase wbc_entity_usage schema:

https://www.mediawiki.org/wiki/Wikibase/Usage

Specifically, the details will be provided on:

• the structure of C aspect records;
• the way L and D aspects are recorded in respect to the operation of the language fallback mechanism;
• the exact difference between the S and T records;
• the contexts in which O is recorded.

The existing documentation from the above mentioned locations, plus the new details are provided in the new central Usage Tracking documentation: https://doc.wikimedia.org/Wikibase/master/php/md_docs_topics_usagetracking.html