In general, it means not processed foods. The edges of the grocery store. Nothing out of a box.
You can add to that, organic. It makes it a bit more complicated. Harder to shop for. And if you aren't following sales, more expensive.
You can add to that Paleo, vegan or some other label. And once again it gets a bit more complicated.
Eating Paleo isn't like what the media wants people to think. It isn't a meat based diet. It's very much a veggie based diet but always with a good helping of fat and protein. The easiest (and in my opinion tastiest) source of healthy fat and protein is meat. Yum. But to eat Paleo you have to give up a handful of things that have been proven to be harmful, like grains, specifically gluten but all grains are cut out if you eat Paleo.
I also cut out dairy. Most Paleo types do. Some call themselves Primal instead of Paleo and they keep dairy. Really it's all a matter of semantics. And finding where you fit on the eating clean scale.
For me, it isn't about fitting into a label. It's about getting away from cheap, unhealthy food. It's hard to know these days with media shoving down everyone's throats what is healthy and what isn't. After all, all cereals are "part of a healthy breakfast", never mind their sugar content and the fact that their nutrients are added by chemicals, not nature. Kool-aid has less sugar than soda, don't mind the Red 40 or Yellow 5. Then there is the whole grains vs enriched wheat flour. High fructose corn syrup. Brominated Vegetable Oil. Aspartame. Nitrates.
And yet everyone still wants you to think you can eat their food product and still be healthy. But it's obvious that's just not true.
*sigh* So how do you know what's healthy? What makes a clean food?
My rules of thumb.
1. If it can be sold without a nutrition label. It's clean.
2. If the food will go bad before the end of the week, even if kept in the refrigerator. Then it's probably clean.
The rest should be eaten sparingly or not at all.
I very firmly believe that our country's obesity problem would start to resolve itself if people ate clean. No more boxed food. No more fast food. Learn to cook for yourself. By the time you wait in line at the drive through and get your meal home, you could have cooked a healthy clean meal for your family at home. And there is a lot less waste from all those packages.
When you eat better, you feel better. And you lose weight wether you mean to or not. Bonus.