Carb counting
Estimating the carbohydrate in a meal to anticipate (or dose for) its effect on glucose.
Carb counting is the habit of tallying the grams of carbohydrate in what you eat, since carbohydrate is the macronutrient that moves glucose most. People on insulin use it to match doses; everyone else can use it to predict which meals will spike them.
Pairing the count with glycemic load and a post-meal reading turns it from arithmetic into insight: you learn not just how much carbohydrate a meal had, but how your body handled it.