Hey Anj,
To put it short, it is basically no carbs at all throughout the week and a refeed on one weekend day. You would eat only protein and healthy fats throughout the week. There are several different variations with the refeed concept, but Keto diets are based around forcing your body to go into ketosis and if you eat even the slightest amount of carb most often the process is thwarted. It takes a lot of self-control to run a Keto diet.