Big Data is nothing but a concept which facilitates handling large amount of data sets. Hadoop is just a single framework out of dozens of tools. Hadoop is primarily used for batch processing. The difference between big data and the open source software Hadoop is a distinct and fundamental one.
Big Data Hadoop brought a radical approach. In Hadoop, the program goes to the data, not vice versa. It initially distributes the data to multiple systems and later runs the computation wherever the data is located.