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>.
AWE shares the confidence of that article: "Naturally, they're spelled correctly here".