The avant-nef gives access to the nef (nave) and is located at the outmost west side of the church.
The grey part in plan (Wikipedia) is the avant-nef.
The picture shows the peculiar avant-nef of the Saint-Philibert in Tournus; it was taken from under the avant-nef, at the entrance to the church, looking in the direction of the chœur (choir).
See also avant-nef and narthex (synonyms).
|Avant-nef - Wikipedia|
|Saint-Philibert - Tournus|