Hors d'oeuvre is a type of food that might also be called starters or appetizers. (Which of these three terms is used might tell you more about the sort of occasion and the people involved than the actual food.)
It is a French phrase, often mis-spelled. As for pronunciation, just do your best: the 's' is silent, and English speakers don't usually bother with the 'vre'.
This page was suggested by the list of "25 of the most commonly misspelled words in the English language", in the article on "spelling" in Garner, Bryan A., The Oxford Dictionary of American Usage and Style, Oxford University Press, 2000; on line at Oxford Reference Online. Oxford University Press, under licence to Hull University. 18 July 2006. <http://www.oxfordreference.com/views/ENTRY.html?subview=Main&entry=t26.e2017>. Although the list claims "25 of the most commonly misspelled words in the English language", it may reflect the American language of the book rather than AWE's experience of English teaching in Britain. Users of AWE may find more use in our categories spelling and spelling common errors.
AWE shares the confidence of the original article: "Naturally, [the commonly misspelled words] are spelled correctly here".