Some of this has been covered in previous posts, but it can't hurt to have some chocolate terms you can comfortably throw around. Here are the basic ones—feel free to add yours in the comments!
Bloom: What happens when chocolate is a) exposed to moisture (sugar bloom) or b) exposed to heat after tempering (fat bloom). Sugar bloom looks like dull blotches and spots that are rough to the touch; chocolate that is sugar bloomed cannot be re-tempered, but can be used in baking, sauces, and pretty much everything else. Fat bloom is streaky/swirly and smooth to the touch; chocolate that is fat bloomed can be re-tempered.
Cacao/Cocoa: Generally speaking, the term "cacao" refers to the raw materials of chocolate before it becomes a finished product—the trees (Criollo, Forastero, and Trinitario), pods, beans, and liquor (pure cacao bean paste, sans sugar etc). Cocoa refers to cocoa powder (the cocoa solids) and subsequently processed products.
Cocoa butter: The fat in the cacao bean. This is released during grinding, and in some cases pressed out of the mass to make cocoa powder. True cocoa butter is ivory in color, melts at around 88℉, and has a neutral taste. Since it melts below body temperature, it imparts a cooling sensation when it melts in the mouth.
Cocoa solids: Everything in the cacao bean that isn't fat; cocoa powder is pure cocoa solids: ground cacao beans that have had most of the fat pressed out of them, turning them into a hard cake which is then pulverized.
Compound coating: A product that may contain cocoa solids, but has replaced some or all of the cocoa butter with other vegetable fats. Also known as "no-temper chocolate," it doesn't fall under the definition of true chocolate.
Couverture: Chocolate which contains at least 30% cocoa butter, which facilitates dipping. The more cocoa butter, the lower the viscosity; non-couverture chocolate is too thick when tempered to achieve the ideal nice thin shell on a dipped confection.
Criollo: One of the three Theobroma cacao tree varieties. Criollo is the rarest, most vulnerable to disease, and therefore most expensive of the three. Criollo cacao beans have the most delicate flavor, and are highly prized by chocolate manufacturers. Most criollo beans come from Venezuela.
Dark chocolate: Chocolate that consists solely of cocoa solids, cocoa butter, and sugar. An emulsifier is often present in small amounts—2 to 5%—depending on the brand of chocolate.
Dutch process: A method of treating cocoa powder with an alkalizing agent to reduce its acidity, mellow the chocolate flavor, and increase solubility. Dutched cocoa is much darker than the untreated variety.
Emulsifier: Usually lecithin, usually derived from soy; the emulsifier stabilizes the chocolate to prevent bloom and improve shelf life, as well as imparting a smoother mouthfeel to the chocolate.
Forastero: The hardiest variety of cacao tree, and the most widespread, the beans tend to be more astringent, requiring longer fermentation times. Forastero are grown largely in Africa, which produces about 70% of the world's cocoa supply; often blended with other varieties to mellow their flavor.
Ganache: An emulsion of chocolate and dairy (usually cream), and often other flavorings such as spices or liqueur. Ganache is the most common filling for bonbons and the only filling for classic truffles.
Gianduja A chocolate that is ground with hazelnuts during processing, incorporating the hazelnut paste seamlessly into the finished product. Supposedly the hazelnuts, cheaper than cocoa, were originally incorporated by 19th-century producers to bring down the cost of their finished chocolate.
Mucilage: The white pulp surrounding the cacao beans in the pod. Gross name, but it's actually delicious. There are many different kinds of drinks made from this pulp in Central and South America, both fermented and non.
Milk chocolate: Chocolate that has milk powder or milk solids added to it as well as sugar. "Dark" milk chocolate, with higher cocoa solid percentages, has gained popularity in recent years.
Nibs: The fermented, dried, cracked and winnowed cacao beans.
Tempering: A process of heating and cooling chocolate in a specified manner to create uniform crystals that are shelf-stable and provide desirable characteristics like snap, gloss, and sturdiness.
Trinitario: A hybrid of criollo and forastero varieties, hardier than the former and with a more delicate, fruitier flavor than the latter. Developed originally in Trinidad, it can be found there and on the island of Java.