De or het reisforum?

The correct Dutch article is:

het reisforum

Rule Words ending in -um and -ium: usually het. See the rule

How to use reisforum

the reisforumhet reisforum
this reisforumdit reisforum
that reisforumdat reisforum
our reisforumons reisforum
your reisforumjouw reisforum
every reisforumelk reisforum
which reisforum?welk reisforum?
a big reisforum / the big reisforumeen groot reisforum, het grote reisforum