A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Gordon,
Thank you for posting back.
We understand that you want to know the maximum number of terms in a term set in SharePoint online, however, we do not have a clear limitation for SharePoint Online but 30,000 is a good number for reference. The limitation should follow the SharePoint server 2013 since SharePoint Online is based on that structure. 30000 per term set.
If you still want to have a confirmed answer, we’d suggest you contact with your Office 365 admin to raise a case and have the phone support to check with PG.
The Office 365 admin can go to Office 365 admin center > click Support > click New service request to raise a new case.
Your understanding and patience will be highly appreciated.
Best Regards,
Sukie