What is the meaning of instance?


I found the following information from Microsoft (see http://technet.microsoft.com/en-us/library/dd309684(AX.50).aspx):

You can install only one GLS layer with the SYS layer in a single instance of Microsoft Dynamics AX . You must install each additional GLS layer in a separate instance. If you require countries that are in two separate GLS layers, you need to implement two instances, each with its own SYS layer and the required GLS layer. The following table illustrates configuration of different instances.

Question: Can somebody explain me what is understood under instance?

Is an instance a separate database or just another AOS server that can run on the same database?

Hope somebody can help.