Translation:A vegetarian does not eat meat and fish.
So there's no point in that word, though. A person who eats chicken would be chickentarean? The point of vegetarianism is to make a distinction because of either ethics or ecology, some kind of variant that includes animals is unethical (and a "pescentarian" diet is worse, because it includes more fish, and since those are much more smaller than cows, for example, that means a lot more animales being killed) and in the case of fish is about half of the plastic in the oceans, so kind of pointless to make a new word for people who eat meat but only from some animals.
It comes from the Bible, which classifies poultry and fish separately from meat, because it considers that animals have four legs, therefore birds and fish are not animals.
Of course, now we recognise that that they all belong to the animal kingdom, so really they are all animals.
Note that the language is very careful to divide animals from living creatures in the water (fish and other aquatic life such as lobsters and oysters), from birds, from insects, and from other "creeping" creatures (moving along the ground) which would include worms and snails.
The "r" can denote the plural indefinite (menneske (person) - mennesker (persons)), the agent of the verb (fortelle (to tell) - forteller (teller)) or the present tense (fortelle (to tell) - han forteller (he tells)).
In this case, "vegetarianer" is the base form. The plural indefinite would be "vegetarianere".