Big Data is term which is used these days to represent data set which is very big is size and such data size can not be handled by one computer. So, for handing such huge (Big Data) set requires many commodity server where data is saved in distributed environment.
There are many platform for Handling such a huge data on distributed computers. These distributed computers also provides processing power so that processing can be done on the system where data resides.
Hadoop is one of the Big Data which is used by various industries.
Check tutorial for complete details at: What is Big Data Platform?