If you're looking for meat with the fewest amount of calories, know what you're measuring, and set some ground rules. "Meat" means different things to different people, and it's safe to say that there are "meats" out there that might not fit your diet.
Let's use pork as our standard meat; 100 grams (about 3.5 ounces) of roasted ham. That's about 225 calories. Compare that to meat from the minke whale, a traditional Japanese dish. The whale meat comes in at a scanty 116 calories per 100 grams, much better than the ham. But it's not hard to think of at least a couple reasons why it's doubtful that minke will be showing up for dinner anytime soon.
In any case, there's no need to go all the way to Japan to find meat with a caloric count far lower than pork. If you hunt, or know a hunter, you might want to consider wild game. Again, there's an ick factor, but game as a whole is typically leaner than anything in the grocery store. Leaner means less fat, and fewer calories. 3.5 ounces of wild rabbit, for instance, has just 114 calories. The same amount of meat from a domesticated rabbit contains 136 calories. It's venison that holds the record for meat with the least amount of calories however, with just 104 in 100 grams.
Here again we face the question of "what is meat?" To many people, nothing that ever had feathers need apply. But if poultry qualifies as meat to you, then there are a few good choices. 100 grams of skinless chicken breast has just 116 calories. An equivalent amount of turkey breast meat has just 104 calories. If you want something more exotic, try ostrich. 100 grams of ostrich leg has just 111 calories.
But, if poultry doesn't qualify as meat, and you prefer your meat wrapped in plastic with a bar code on it, then beef is probably your best bet. It has to be lean beef, with all the fat cut off, and 3.5 ounces of it will still contain 176 calories. That's still a lot.
But, there's always fish.