In .NET Framework languages such as C#, you can use the same LINQ syntax and paradigm that you already use with LINQ to SQL.
Why is this important?
LINQ to AX makes it easier to interoperate with Microsoft Dynamics AX data from your C# program.
How was this performed in previous versions?
Without LINQ to AX, the primary way your C# program can access table data is to call the methods on a C# class that is a proxy to a table.
My above blog is based on Microsoft's Official information.