Paleo style eating focuses on natural foods (as opposed to processed foods) that might have been available to our ancestors. Let's call it the Paleo Style Eating because most of us don't like the word "diet," even though a diet is just what you eat in the course of a day.
Here is a handy list of the "Paleo Foods" and the "Foods to limit, avoid". If you go to the link, you will find this in a nice, printable form. For those of you who like to read the research background, page 2 also has a list of references that cover how Paleo eating relates to immune system to cardiovascular disease.
lean meat (beef, poultry, pork)
unsalted nuts and seeds
Foods to avoid or limit:
Dairy foods (butter, cheese, milk, yogurt, etc.)
Grains (barley, corn, oats, rice, wheat, etc.)
Legumes (all beans, soybean products, lentils, etc.)
Starchy vegetables (potatoes)
Salty foods (processed meats, condiments, etc.)
Sugary soft drinks
High sugar fruits, dried fruit, all fruit juices
Fatty meats (bacon, lamb chops, chicken thighs, wings, and legs, etc.)