"Clean" is pretty well understood as what's left after you finish an elimination diet.
As i just described it can be different for different people but in general, super high fat, super high carbohydrate, meals that are too large or too frequent, too much alcohol, lots of additives, lots of candy or cake, too many heavy metals from fish, too much fried food, too much low quality processed foods including cheap oils that has gone semi rancid, corn syrup, various carcinogens are all agreed upon across various a large spectrum of diets from Vegan to Paleo including nutrition research.
It probably also depends on ones own gut flora.
Pausing eating or just eating a pretty bland diet without above "luxuries" and you definitely get less of these things, that's partly why fasting works for a lot of people.
Although I don't know any diet that would be "clean" compared with a water fast...
Vegan perhaps?
It's neither bs nor meaningless. It intuitively describes a good diet if you have a basic knowledge of food and diet. It basically means "what is good for you". What would you describe as "clean", deep fried butter or broccoli sprouts? See how it's intuitive?
The only intuitive difference I see in those scenarios is that one has less calories and less fat (which are obviously both essential components of any diet).
Your lack of understanding of the context of use, and underlying meaning, is nobody's problem but your own.
Perhaps you should have asked what He meant by clean, because clearly you don't understand.
https://www.primalorganicmiami.com/eat-clean-miami/ As this website says "There is not a strict definition for “eating clean”. I still assert clean eating is meaningless.
I'm not against healthy eating. But "healthy eating" or "clean foods" don't have definitions.
Think of it this way, there may not be a nailed down definition of “clean” or healthy” eating. However, it gets you in a “range of uncertainty”
Is McDonalds clean? No. Is Pizza clean? Nope. Is brown rice clean? Maybe. I should ask what they mean by their usage of clean.
Have I made my point a little bitter? I view usage of vague terms like that not as useless, but as “gets you close to the target without getting lost in the weeds.”
Hope this helps.