To answer this question, let’s turn to the source of all modern knowledge, Wikipedia :-
Data-driven journalism is a journalistic process based on analyzing and filtering large data sets for the purpose of creating a new story. Data-driven journalism deals with open data that is freely available online and analyzed with open source tools. Data-driven journalism strives to reach new levels of service for the public, helping consumers, managers, politicians to understand patterns and make decisions based on the findings. As such, data driven journalism might help to put journalists into a role relevant for society in a new way.
The rest of the Wikipedia article explains the process of data journalism neatly summarised in this graphic :-
The British tabloid The Guardian is currently the industry leader in this field, devoting a section of their news for data journalism. They even encourage the public to come up with their own data stories, making educational resources and guides available to the public via their online portal.
There’s an article by The Guardian explaining data journalism in ten points :-
1. It may be trendy but it’s not new
2. Open data means open data journalism
3. Has data journalism become curation?
4. Bigger datasets, smaller things
5. Data journalism is 80% perspiration, 10% great idea, 10% output
6. Long and short-form
7. Anyone can do it…
8. … but looks can be everything
9. You don’t have to be a programmer
10. It’s (still) all about stories