It is nothing but the flow of data from one part of the application to the other part of the application to complete the operation and get expected result any program will have its own way of working and its own architecture.
In Microsoft dynamics ax, there is a 3-tier infrastructure with a database server, an AOS and a
client.
In the above figure client is called as Morphx, this is IDE which is used to communicate with AX server . custom AX development and modification is done with its own IDE , Morphx.
Morphx is an integrated development environment in ax that allows developer to graphically design data types, base enums , tables, queries , forms, menus and reports.
In AOS is a core component of the Microsoft dynamics ax 2012 installation and is installed by using setup . An AOS enforces security , manage connections between clients and the database .
Finally backend tier is used to store the data . AOS will not store any data except execution business logic and communicate with backend to get and store data . Usually SQL server 2005 is used for ax 2009 and SQL 2008 used for AX 2012 to store data.