A type of dish served at the beginning (depending on the usage of the term) or prior to the official beginning of the meal. These are dishes that are typically finger foods. In common vernacular, hors d’oeuvres are appetizers. Technically speaking, though, there is a difference.
As indicated before, hors d’oeuvres are served prior to the official beginning of the meal. Appetizers are typically served to signify the beginning of the meal or after the official beginning. While hors d’oeuvres can be served prior to an official dinner, they are not used to signal that a full blown meal is to follow. Appetizers, by their very nature, are meant to accompany a dinner, kind of like the vanguard of an army.
Hors d’oeuvres, outside of a formal dinner setting, are finger foods that typically accompany cocktails. Thus, they are the ideal snack food for social gatherings where mingling is encouraged. This includes the following settings: wedding receptions, conference receptions, galas, fundraisers, and many more such occasions. In some cases, they are smaller than appetizers, but this can vary as well.
If you are still confused by the concept, think of it like this. You are at a wedding reception for some people that you don’t know that well. Which food would be better for the setting: deviled eggs or a big ol’ honking bowl of chili?
Hors d’oeuvres may be hot. They may be cold. It really depends on the dish. Likewise, they are not defined by the types of textures used. They are dependent upon size, social context, and being finger-oriented. Additionally, you can have the option of choosing which one you consume.
As with a lot of culinary terms, this term is French in origin. The transliteration of the term is “outside the work”, and the term’s modern usage can be traced back to the late 17th century. I should note that, according to Encyclopedia Britannica, the term was previously used in an architectural context as far back as the late 16th century. As such, it is best to understand the function of hors d’oeuvres as occurring within the context of a work of art/performance.
Compare with amuse-bouche.