"He eats chicken or fish."
Translation:Lui mangia pollo o pesce.
It is the subjunctive mood of the first, second and third person singular present tense of essere
When to use the subjunctive is the subject of later lessons
Hi Kate! Oppure and o are taught together so users can learn the pattern from the example sentences :) This is the way anybody learns their own language as well, right? A child in Bologna might think "ma che cavolo vuol dire antitesi?" but after seeing it a few times in context it begins to make sense. We're always open to suggestions if you have ideas to make the process better!
Probably for the same reason that we do not say "the chickens" in English when asking if someone eats chicken i.e when describing a category of meat there is no need for a definite article or the plural.
i polli could be used in either a generalisation about ALL chickens, or a reference to some particular chickens, but neither of those is the case here.
you could use the article with a singular noun to reference the general category of chicken/fish. oppure you can omit the article to reference some nonspecific chicken/fish. but the plural is a reference to some specific chickens/fish (those in the refrigerator maybe) and that doesn't fit with the english sentence.