You can find an extensive explanation in our docs (section 3, business and technical context)

A short summary:

• The business context concentrates an pure business or domain interactions of the system with its environment. You will often find domain terms for external interfaces, no technology.
• The technical context shows hardware, technical infrastructure, technical protocols, network details or similar information concerning the system and its (technical) environment.

Especially in embedded or hardware-related systems, the technical context is an important perspective of architectural development.

Especially in information or decision-support (data-warehouse etc) systems, the technical context is often omitted.

Personal experience (from Gernot): For information system, defer the technical information to the deployment view (arc42 section 7) instead of creating and maintaining a technical context. I survived many years and many commercial projects without ever creating a technical context - although you should never (!) start developing systems without having a clear understanding of your business context.