As Fran says, we all have our own definition of clean. To me, eating clean means eating
mostly real, unprocessed foods rather than packaged processed foods. So I'll have fruit and cottage cheese rather than a yogurt with added ingredients and artificial sweetners. I do eat things like canned tomatos and beans, and frozen veggies, but I try to have most of what I eat start as recognizable as food.
I don't eat cake, cookies, cchips, ice cream or candy as a part of my plan. (That's not to say I never slip, or that I didn't eat a piece of cake on my birthday - I did.) I don't beat myself up over a slip, but rather get myself right back to eating on plan.
There's a thread in the food section about whole foods which has lots of good ideas for eating real food.