hors· d'oeuvre (pronounced or-DURV) is a noun. A small portion of a tasty food served as an appetizer before a meal or as at a cocktail party. From the French, and literally means "outside of work"...
It's a variety of appetisers served before a meal.
They are the small appetizers served before the entree of a meal.
That is the correct US plural spelling "hors d'oeuvres" from the French hors d'œuvres (which is singular or plural)
No caps needed. It's a common noun. Of course, you'd capitalize the H if it was the first word in a sentence.