Meditation is also being in tune with your body: your breathing rate, heart beat, body temperature etc are all things that affect your relaxation and state of mind. A part of meditation is paying attention to your breathing rate and breathing a certain way to focus your energy in a positive manner.

I believe meditation to be the focusing of one's energy upon a specific task. When meditating, a person typically clears his or her mind of everything. This clearing of the mind allows one to focus on something very specific (typically breathing).

One could, essentially, use meditation to focus upon a singular act. Perhaps one is wanting to study. In order to do this, the mind must be clear of everything irrelevant to studying. The person will then focus upon the task at hand.

I think meditation can be as simple as just taking a time out to think and/or clear your mind. So often, we - adolescents, adults, everyone- go a whole day without any true quiet time to think. There are always distractions- many times in the form of electronics like a phone or computer. People who don't take time out to clear their mind or think become so attached to those distractions and don't know how to function without them. Therefore, taking a purposeful moment to meditate can be very beneficial and can help a person less susceptible to distractions.

Often the term meditation is ascribed with two meanings. One definition sees meditation as a sustained mental focus which can include action (yoga, making music, etc.) and which also may be characterized by a continued contemplation of a single idea. 

The more strict definition of meditation sees the act as one of intentional inward focus wherein the mind contemplates itself. The idea is to attain a single-mindedness and a special kind of internal quiet. 

Either way you look at meditation, the practice can be very beneficial to people who have trouble focusing. Meditation strengthens mental discipline and that can't hurt.

To me, meditation is the practice of clearing one's mind of everything except a given object or thought.  I suppose that that sort of mental discipline would be helpful to some degree in allowing teens (or anyone else) to block out distractions and attend to a given task like studying.