What are Labels in Microsoft Dynamics AX

The labels in Dynamics AX are a way of translating all user visible text by only referencing to a label ID in the code. Each language is represented by a language-specific label file within each label module. These label files consist of the label ID and the text for that label in that specific language. The label files are stored in the application directory and have the file extension .ald (Application Label Data). When opening a label file in a text editor you can see labels listed below:
@SYS390 Quantity that is not yet cost accounted in the BOM unit.
@SYS400 Create and compose serial numbers automatically.
@SYS403 Finish must be greater than start.
@SYS418 Transfer customer information?

This means that if you write @SYS403 in the label-property of a field in AX it will display Finish must be greater than start. to the users viewing that field in a form or report, if they are using the language code en-gb (as this was taken from the label file AxSYSen-gb.ald.)

To create a new label file, simply start the label file wizard from the Microsoft Dynamics AX button (Alt + M), navigate to Tools | Development tools | Label file wizard, and run through the three self-explaining steps of the wizard.

Your label file will then be named AxXXXen-gb.ald, where XXX is a three lettered abbreviation chosen when walking through the wizard.