SDL Trados Studio
SDL Trados GroupShare
SDL Trados Business Manager
SDL Trados Live
SDL MultiTerm
SDL Passolo
SDL Speech to Text
SDL Managed Translation - Enterprise
SDL MultiTrans
SDL TMS
SDL WorldServer
Translation Management Connectors
SDL LiveContent S1000D
SDL Contenta S1000D
SDL XPP
SDL Tridion Docs
SDL Tridion Sites
SDL Content Assistant
SDL Machine Translation Cloud
SDL Machine Translation Connectors
SDL Machine Translation Edge
Language Developers
Tridion Developers
Tridion Docs Developers
Xopus Developers
Community Help
SDL User Experience
Language Products - GCS Internal Community
SDL Community Internal Group
SDL Access Customer Portal
SDL Professional Services
SDL Training & Certification
Style Guides
Language Technology Partner Group
SDL Academic Partners
SDL Enterprise Technology Partners
XyUser Group
ETUG (European Trados User Group) Public Information
Machine Translation User Group
Nordic SDL Tridion Docs User Group
SDL Tridion UK Meetup
SDL Tridion User Group New England
SDL Tridion West Coast User Group
SDL WorldServer User Group
Tridion Docs Europe & APAC User Group
Tridion User Group Benelux
Tridion User Group Ohio Valley
SDL MultiTerm Ideas
SDL Passolo Ideas
SDL Trados GroupShare Ideas
SDL Trados Studio Ideas
SDL Machine Translation Cloud Ideas
SDL Machine Translation Edge Ideas
SDL Language Cloud TMS Ideas
SDL Language Cloud Terminology Ideas
SDL Language Cloud Online Editor Ideas
SDL Managed Translation - Enterprise Ideas
SDL TMS Ideas
SDL WorldServer Ideas
SDL Tridion Docs Ideas
SDL Tridion Sites Ideas
SDL LiveContent S1000D Ideas
SDL XPP Ideas
Events & Webinars
To SDL Documentation
To SDL Support
What's New in SDL
Detecting language please wait for.......
I would be explaining it here, however, I think the best information source in this case is still Microsoft itself:
Microsoft Developer Network - Service Principal Name 
I try to explain it as simple as possible :)
 
In short:
It enables you to use the Windows Authentication method using the mutual Kerberos authentiction (See Microsoft TechNet: What is Kerberos Authentication?)
More detailed:
You set a Service Principal Name (SPN) on a specific server for a service account that is responsible for managing this service to allow the handling of permitting the mutual Kerberos authentication.
Therefore, to use the Kerberos authentication, it is required for the Windows security to determine the (user-)account that a service is using. This is realized by registering the Service Principal Name for the server and the (user-)account which the service is using.
For Windows authentication feature to work on the SDL Trados GroupShare server, you need to set a Service Principal Name (SPN) to identify the account running Trados GroupShare services with the Fully Qualified Domain Name (FQDN) of the web application.
Before you begin you need an account that has Domain Admin permissions or has the Validated write to service principal names permission delegated.
setspn -S http/servername serviceaccount
setspn -S https/servername serviceaccount
Where servername is the fully qualified domain name and serviceaccount is the account running the Trados GroupShare services. This is an example of how the syntax could look like:
setspn -S http/gsserver.sdl.com global\adminuser