Is meditation and concentration the same?

I have often pondered and tried a lot to understand the actual difference between meditation and concentration or are they terminologies that can be interchangeable.From what I have read and understood i believe that concentration is all about enabling the mind to focus on one particular subject. Here the center core of the subject is one but there can be varied similar and dissimilar thoughts regarding it. Meditation or also known as Dhyanam is more intricate and complex version of concentration. During meditation the mind is fully conscious about the entire process and it is an exercise of the will. Meditation can also imply that there is complete concentration on spiritual ideas and the individual goes deeper into his thought and can rise above the normal worldly ideas. I also believe that one cannot attain this state of complete meditation in a day or two. It surely requires immense practice and can be obtained only at a particular center of consciousness.