De or het vetvertering?

The correct Dutch article is:

de vetvertering

Rule Words ending in -ing: almost always de. See the rule

How to use vetvertering

the vetverteringde vetvertering
this vetverteringdeze vetvertering
that vetverteringdie vetvertering
our vetverteringonze vetvertering
your vetverteringjouw vetvertering
every vetverteringelke vetvertering
which vetvertering?welke vetvertering?
a big vetvertering / the big vetverteringeen grote vetvertering, de grote vetvertering