How to measure a cup of "solid" ingredient? I was reading a recipe in which it was mentioned among the ingredients "8 cups of broccoli florets". Measuring by "cups" is for liquids, right? For solid ingredients, are we measuring the "weight" of the ingredient?

How to convert "8 cups of broccoli florets" into kilograms/grams?
It's asking for exactly what it says: 8 cups of broccoli. Measuring by volume is certainly best-defined for liquids, but it works fine for solids too. It works best if you have a large measuring bowl - or just a bowl that you happen to know is around 8 cups (two quarts, about two liters). Or you can just guess by eye, knowing how much volume that is. A recipe with broccoli isn't going to fail if you're off by a bit.

(If you really prefer weight, this nutrition data says a cup chopped is 91 grams, so 8 cups might be a bit over 700 grams.)