The hors d'oeuvre as a genre is limited only by the imagination of the chef. After all, as long as a food can be held between thumb and index finger and consumed in a couple of bites or less without undue dripping or flaking, it qualifies to be served with cocktails at a pre-dinnerish hour. And so many different countries have their own versions of hors d'oeuvres, which contribute to the American repertoire. China has dim sum. In Spain, people sip sherry while they nibble on tapas. Italians enjoy antipasto. And the Russians' zakuski is practically an art form.

But from the point of view of the guest with martini in hand, all that variety is just the spice of the party. It's pretty easy to tell what you're eating because, even if it looks mysterious, there's usually a bow-tied server nearby to murmur "country pate" or "smoked trout mousse" in response to a querying look. However, there are a few cocktail party vocabulary words that have to do with presentation more than content, and you may find them helpful the next time you wander casually over to the hors d'oeuvre table to contemplate the offerings.

It looks like a little open-faced sandwich. It's a canapé. This is probably the most versatile and classic type of hors d'oeuvre. Canapés can be served hot or cold; they can be utterly elaborate or sophisticated in their simplicity. They don't really even have to be open-faced sandwiches (although they do have to be diminutive and contain sliced bread). An item made with paper-thin cross-sections of onion between two pieces of mayonnaise-spread bread would be a tea sandwich if served at 3 p.m. with a steaming, steeped beverage as accompaniment. But if it's 7 p.m. and you're holding a martini, it's a canapé.

In general, a canapé is made by cutting a slice of bread into a bite-sized shape (square, circle, diamond, heart, clover...whatever), putting a thin layer of savory spread on it (mayonnaise, butter, compound butter...you name it), adding a thin layer of something (smoked salmon, pate, tomato, anchovies...according to the chef's whim), and topping it all off with a teeny garnish. Some particularly fancy ones have numerous toppings that have been cut into complex shapes and arranged to form designs. Hot canapés are made in pretty much the same way, but with toasted bread slices. They are sometimes called croustades or crostini (the latter being Italian for savory tidbits on toast).

The toppings on canapés and the types of bread may vary, but there is one constant. You'll never encounter a crust on the bread in your canapé; It has always been removed, as if the guests at cocktail parties have all reverted to their first grade selves, the kids who thought bread crusts were icky and envied the lucky few whose moms packed crustless baloney sandwiches in their lunchboxes.

It's got a crust. Canapés may be crustless, but there are plenty of crisp and flaky, crustful pastries on the hors d'oeuvre menu. The tartlet, for example. Its half-dollar-sized crust usually holds a savory, custardy filling, like a quiche. A tartlet shaped like a boat is called a barquette.

Versatile puff pastry appears in disguise after clever disguise on the hors d'oeuvres tray. Long, thin sticks of puff pastry sprinkled with cheese are most commonly known as cheese straws. Sticklers for nomenclature might prefer the name allumettes, though. If the dough is twisted to form long spirals before it is baked, a cheese straw might more properly be called a sacristain. And if the dough is spread with filling, folded over, and baked before being cut into straws, you're talking about dartois.

There are even more uses for puff pastry. When circles of the dough are baked, they rise into cylinders that can be hollowed out, filled with whatever suits the chef's fancy, and presented to the guests by name -- bouchées. Talmouses are little bundles made by pinching the corners of a square piece of puff pastry together to enclose a lump of filling.

Pâté; chou is used to make a couple of popular hors d'oeuvres. When baked in blobs (the finished products look like little heads of cabbage -- or "choux") and hollowed out to hold fillings, they are known as choux puffs. If there's no filling, but cheese has been mixed into the dough before baking, they are cheese puffs.

And then there are the en croutes, food wrapped in brioche dough and baked until golden. Brie, pâté, and saucisson are all often served en croute.

It's served on a stick. That is, the hors d'oeuvre is en brochette, or skewered. Grilled shrimp (or any grilled, bite-sized pieces of meat) are often served this way, as are tortellini. A relative of the skewer, the toothpick, is often used to hold layers of folded or rolled food together. Toothpicks have a more retro appearance than skewers (especially when the ones with colorful frills at the end are used). Many of the classic hors d'oeuvres of the fifties were held together this way. (Rumaki is an example of such a classic. It is made by wrapping a piece of bacon around a marinated chicken liver and a slice of water chestnut, then baking the whole thing until the bacon is crisp.)

At a true, classic cocktail party, only hors d'oeuvres that are compact, easily plucked from the tray and popped into the mouth are served. Not a fork or a plate is to be found. At such events, skewers and toothpicks are the closest you can get to an eating utensil. It is incumbent on the hosts, by the way, to make it clear where the used bits of wood should be discarded. In case they fail in this task, you are perfectly within your rights to abandon skewers in ashtrays and on stray cocktail napkins (the same holds true of olive pits).

It's a bunch of vegetables, with dip. Those are crudité ("crudité" means "raw food" or "salad"). Popular dips include aioli, bagna cauda (a Piedmontese specialty with olive oil, garlic, and anchovies) and hummus. Just don't dip your carrot stick twice -- that's frowned upon. Other vegetable-oriented hors d'oeuvres you are likely to encounter are the stuffed variety. Cherry tomatoes, Belgian endive leaves, celery, snow peas, mushroom caps, hollowed-out cucumber slices, and small new potatoes are all good vehicles for a dab of crème fraîche, herbed cream cheese, or smoked salmon mousse.