The term “digital minimalism” can be explained through two complimentary yet different perspectives:
The first perspective is from that of the consumer, which has been described well in the other answers; the practise of minimising the digital clutter in ones life.
The second perspective is that of the creator of digital content, products and services.
Amongst artists and designers Digital Minimalism is a growing branch of the Minimalism movement of the 1960s.
In this sense Digital Minimalism is the conscientious design practise of paring down a product or service, across all customer facing touch points, to its essential elements and reducing the strain of “digital clutter” on the consumer.
More discussion on Quora.