A technical story is one where the main stakeholders are the engineering/infrastructure team/leadership. The end-user benefits only indirectly from such a story. Technical stories often are non-functional requirements.  Non-functional requirements include security, performance, maintainability, usability, refactoring, infrastructure,accessibility, compliance, reusability.  (Look up Non-Functional Requirements).  

https://rgalen.com/agile-training-news/2013/11/10/technical-user-stories-what-when-and-how