Big words that do well in marketing. They make sports something that is ultra-modern and based on scientific medical evidence. Then it has to be good and healthy?

Cardio is what concerns the heart.
Fitness is a buzzword for intense exercise or sports (to burn fat, improve fitness or muscle mass). It comes from fit: in good condition, and fitting.

Workout: intense physical exercise or training. (It also stays for calculation and others derived meanings.)
Routine stands for experience and skill.

Cardio training programs are adjusted to the measured pulse. By continuing to move at a constant heart beat one wants to build fitness or lose weight.

CardioDanceCardio training can ensure that your metabolism will work faster and you burn more calories (even at rest). There is a difference between "normal cardio training" and "cardio workout to lose weight."
If you want to lose weight (fat burning), you have to keep the heart rate between 60 and 70 % of your maximum heart rate. Only then you burn mostly fat and carbohydrates (sugars).
A rule of thumb without devices, if you can talk during training, without getting out of breath, then your heart rate is good to burn fat.
The maximum heart rate (100 %) is calculated by subtracting your age from 220.

Your body uses in efforts first the sugars in your glycogen level, present in your blood, liver, and muscles. Thereafter, the body consumes those that were saved as a backup.
If you want to consume this fat as energy with this exercise, you should use as little as possible from the first natural energy source (carbohydrates or sugars) in your body. Your body then goes to the second power source.

During cardio exercises it is wise to drink regularly to prevent dehydration. If you want to lose weight you should not eat abundant food after cardio.

Three or four times a week, about 30 minutes of training would have a good effect. Self-discipline and perseverance are also needed.

And as always: do everything in moderation, and get plenty of variation.