I've heard it means "sport package" on the E series. How do you know if you have this package? I'm looking at a 2007 E350 w/18" wheels and two tone interior. The salesman told me the interior is Avantgarde???

Thanks.

 

Avantgarde means " people or works that are experimental or innovative, particularly with respect to art "

Therefore, I expect the salesman is trying to describe an interior which is an acquired taste or slightly "left field"

 

Here in Canada, the E class is only available as Avantgarde, just for the 2009 MY since the E class comes in only one version (fully loaded with no options). It is offered for one reason--it is the last of the current body style and MB is unloading all of the old model.
Otherwise for a 2007 E class, he is just using it as a descriptive term. It does not normally mean 'sport package'.