Net Carbs and Total Carbs
Two people can both say they eat twenty grams of carbs a day on keto and mean quite different things, because one is counting total carbohydrate and the other is counting net carbs. Knowing the difference, and which to follow, saves a lot of confusion.
The basic idea Net carbs are the carbohydrates that actually raise your blood sugar and so matter for ketosis. You arrive at them by taking the total carbohydrate in a food and subtracting the parts your body does not absorb as usable sugar, chiefly fibre and most sugar alcohols.