You can save any expression for reuse. You can share expressions you saved with other users.
You cannot save a calculation. The calculation becomes a property for the current feature class in the current model, but is not saved back to the original data store.
The next time you save or load an expression, this location will be displayed by default. To share this saved expression with another user, send that user the file from this location.
By default, the expression file name is the first element in the expression. All expressions use the file extension .fdq.
The last location you used to save or load an expression is displayed by default. You can navigate to a different location.
The saved expression replaces whatever you entered in the expression area. Click OK to apply it.