The anatomical position is a reference point.  This point is used by doctors, personal trainers, therapists and various other professionals and even perhaps you without knowing it!

What is the anatomical position?

Its a reference point as said above.  The anatomical position is the human body with the standing position, feet together, arms to the side, palms facing forward, and an anterior (front view) view of the body.

Notice I am standing up, feet together, palms facing forward.  

Why is this important?

Because a common set of terms must exist for comparison.  Trainers would be lost without these terms.  

What terms can be used from the anatomical position?
Terms such as anterior, posterior, superior, inferior and many other terms

How are these terms useful in exercise or fitness?

Lets say your doing shoulder shrugs.  You are doing inferior and superior movement of the shoulder girdle.  Yes, I understand its not absolutely crucial for the common person who exercises recreationally to know this, but think of it as an added bonus for knowledge.

Where can I get more information about directional terms such as the ones mentioned above?

For more terms, please be sure to check out the anatomical terms of direction, the anatomical terms of movement and the planes of the body.