MapReduce is not a "program", it's a paradigm. It's helps you to structure and implement your code in a way that it will be executable on scale. Having your code executable on multiple machines with possibility to scale on much bigger clusters called "effective".
Thank you Viktor , i just started learning big data just few days back . so far its seems to me quite interesting but as beginner it's also a bit confusing .i would appreciate if you could recommend any books or etc regarding big data
Dear Zakariye, there are many many materials and books available online on the topic of big data. What I can do is to provide you with link to own collection of resources I use from time to time, here it is - http://vdmitriyev.github.io/blog/own-collection-of-resources-related-to-data-science-and-buzz-around.html