These are some of the abbreviations, numbers, and amounts you might see referenced now and then:
ABV - Alcohol by Volume. For beers, this usually between 4% and 12%. Yes, this indicates how much alcohol is in the bottle, but this value also tells you something about the beer itself. The higher the alcohol, the more rich and complex the beer tends to be. High alcohol beers also often have a thicker, smoother mouthfeel.
IBU - International Bittering Units. This refers to the amount of isomerized hop resins in the beer, and is given in parts per million. Essentially, the higher this number, the more hoppy the beer.
This can be misleading though, because your perception of bitterness might be different based on the other ingredients in the beer. In other words, you might think a pale ale tastes hoppier than an imperial stout, even though the stout might have more IBUs.
FG - Final Gravity. This is a measure of the density of the beer at the time of bottling and is used to determine the alcohol content of the fermented beer. Sometimes you'll see the term Apparent Attenuation (AA), which refers to the difference in original and final gravity. (Original gravity is taken prior to fermentation)
Plato - This indicates the ratio of fermentable sugars to water in the beer. It's based on the specific gravity (the gravity/density of the beer at any given time), and is given in degrees.
Lovibond, SRM, or EBC - These are all terms that describe the color of the beer. The Lovibond system compared vials of the beer to vials of colored liquids, but this method has been largely replaced by more modern technology. SRM stands for Standard Reference Method and uses light meters to measure color intensity. EBC (European Brewers Convention) units also uses a light meter, but is based on a different scale. For all scales, the higher the number, the darker the beer.
Bottling and Expiration Date - If they list this at all, beers will generally give one or the other of these dates. With the exception of higher alcohol beers meant for aging, beer is generally good for about one year after the bottling date. If the expiration date is given, this means that the brewer feels the beer will not be at its best after that date.
Knowing these terms isn't going to fundamentally change your experience of drinking a beer, but they do give some interesting insight into the beer's history and character. And at the very least, they're fun terms to throw around at your next dinner party!