Thanks for the writing props there Arden. The meta part of the word is for metabolic and that has to do with your energy systems. You have certainly heard and used the word metabolism and have a sense for slow and fast metabolisms. Some people walk by a bakery and gain two pounds and others shove everything they can get their hands on down their pie hole and never gain a pound. Metabolic - energy systems.
The con is easy, that's just conditioning and the contraction metcon is shorthand for the CrossFit methodology for improvement of the cardio vascular and cardio respiratory systems through a variety of functional exercises executed at high intensity. The program does wonders for much more than just your CV/CR systems but were just discussing metcon here.
Short energy systems course:
Creatine Phosphate or Phosphogen up to about 10 seconds of pedal to the metal, all out exertion. One rep max sort of thing.
At the other end of the spectrum is the Aerobic system which (assuming you are not working out as you read this) you are using right now. You can be in this energy system for the rest of your life. In an exercise sense it is at an effort level you can sustain for about 90 minutes before you exhaust your glycogen supply and have to refuel. How hard you can go is influenced directly by training and there are many endurance athletes who can do 5:30 miles and still be aerobic. I hate those people. The term LSD (Long Slow Distance) is the typical protocol for aerobic work where you are working at a low output for a long period of time.
The CrossFit arena is the Glycolytic energy system where you hammer your way to and through your lactate threshold at an effort level sustainable for only 2 minutes or so. The CF protocol has you change the demand on the failing musculature after some number of reps or time by moving to a new exercise while the CV/CR system is still being taxed. This allows for metabolic conditioning at a far more intense level than you could ever hope to achieve through a single mode of exercise because of the predictable onset of muscle failure at high levels of exertion.
If you go to the FAQ's and look up the notes from the CrossFit seminars the subject of energy systems is covered in far greater detail and ought to answer your question better than I did here.