Training for specificity simply means setting your desired training and exercise goals specific to the results you are trying to obtain.
It makes no sense for a runner to swim if they want to improve their running time. If you want to build your best physique, it makes no sense to do cardio every day because a more resistance-based training plan will build muscle to improve overall body composition.
Your first step when putting an exercise or training plan together, is to ask yourself, ‘What is the goal?
Once you establish this, you can build and design your plan tailored to suit your goal based around exercises that are specific to your sport.
You can then adjust nutrition based on your plan. If you are wanting to run 50km weekly, you will require an increase of carbohydrates to fuel your training, whereas if you are wanting to lose body fat, you will need to make a reduction in carbohydrates.
Identify your goal and then train specifically to it to maximize your results.