The meaning of “vore” according to Wikipedia:
Vorarephilia (often shortened to vore) is a sexual fetish and paraphilia where arousal occurs from the idea of being eaten or by the process of eating. The fantasy may involve the person being swallowed alive, and may or may not include digestion.
And the “giantess” bit should be self-explanatory. This site is for people who like to fantasize about giantesses eating people, being eaten by a giantess, or being a giantess and eating people.
So there you go.