The three big general goals people usually have when it comes to fitness and nutrition, easily explained.
Maintenance = Eating approximately the same amount of calories you burn in order to keep the same weight. You can easily find out how many calories you get to eat a day through various calorie calculators.
Cutting = Eating fewer calories than you burn in order to lose fat. It's an intentional weight loss protocol followed quite precisely in order to make sure that only fat is lost and all muscle mass is maintained.
You start a cut by first determining your maintenance calories. Being in a 10–20% calorie deficit is most recommended, so you’ll take 10-20% off this maintenance number.
A sustainable and healthy rate of weight loss is around 0.45–0.9 kg per week, followed for a maximum of 6-12 weeks.
For the record: starving yourself so you’ll lose weight quickly is not meant by cutting. Eating way too little calories will also make you lose much muscle. Less muscle = lower metabolism, which means that when you start eating normally again, your body will gain weight faster than you’re used to.
Bulking = Eating more calories than you need, in order to put on weight, then building muscle via resistance training. The goal is to gain bigger muscles.
A bulk is also started by first determining your maintenance calories, but here you top your daily calorie intake with 10-20%.