My suggestion of un buffet is not that good, finally, as un buffet usually includes starter, main and dessert. It's is a real meal where you help yourself.
About the suggestions made, here are the way I understand the terms: Un apéritif is supposed to precede a real meal (appetizers) Un apéritif dînatoire it is intended to be copious enough to replace a meal (appetizers, finger food) Un cocktail is a classy apéritif (more sophisticated food and drinks).
Reconsidering Emilyrose's question, cocktail dînatoire would probably fit, because hors-d'oeuvre reception (I bet such a French noun to refer to a reception implies something quite refined ).
The mods will probably remove the links you gave, as they are commercial ones.