Starlink is a constellation of thousands of satellites in low earth orbit being setup to provide low-cost, high-performance Internet access anywhere in the world. Tom Praderio, a SpaceX firmware engineer, said during live launch commentary "This system, if successful, would provide people in low to moderate population densities around the world with affordable high-speed internet access, including many who have never had Internet access before".
Unveiling the project in 2015 Elon said "The focus is going to be on creating a global communication system. In the long term, it will be like rebuilding the internet in space. The goal will be to have the majority of long distance internet traffic go over this network and about 10% local and business traffic."
In June 2019 Elon said the value of Starlink is to provide low-latency, high-bandwidth internet access to the sparse and moderately sparse and relatively low density areas. Rural and semi-rural places that don't have any or any adequate internet access are optimal and will target 3% - 5% of people in the world. It is not well suited for high density cities.
SpaceX has permission to deploy up to 11,943 satellites and is requesting permission to deploy 30,000 satellites in other orbits partially replacing the existing authorization. See below for more details.