Paleo or primal nutrition means eating the way our evolutionary ancestors ate, prior to the agricultural revolution. Or, as I like to say, the way a caveman would eat (and exercise). This means a lot of protein and fat and not too many carbs, so it is similar to low carb diets, but different, too. Some Paleo diets focus on eliminating the "Neolithic Agents of Disease," or NADs. NADs are found in grains, sugars, and processed oils. Further, if we shouldn't eat grains, then we shouldn't eat animals who have eaten grains, either. They advocate eating only pasture (grass) fed animals. Grass fed beef, for example, is substantially more expensive than corn fed beef. They also advocate eating "pastured eggs," or eggs from free range chickens.
But it is more than that, too. Rather than try to explain, I will link to two great sites and a video that explains Paleo or primal eating.
The Archevore site is a great place to start. By Kurt Harris, M.D., who also has some really interesting articles at the Psychology Today web site.
Mark's Daily Apple is a great site with a lot of information by the guy who wrote the book, Primal Blueprint. Here is his Primal Blueprint 101 page.
Finally, this video actually explains the whole Paleo eating philosophy quite well. That is, if you like blue grass music.
For the record, I am following a low carb diet, not a Paleo or Primal diet, but there is a lot to learn at these web sites, information I have found very useful.