Big data is a field or term which refers to analyse or extract information or deals with extremely large data set which is both structured and unstructured, that is too complex to handled by the traditional application softwares.
Example: larger amount consist of billion, trillion etc. records of millions of people getting from websites, social media, personal electronics apps, customer center, mobile and so on.
These type of large, voluminous, complex set is handle by specifically designed software. Many software-as-a-service (SaaS) companies handles this type of large data set which is stored in database.