Iridium is a LEO satellite constellation which provides high-quality voice and data connections across the entire planet. The constellation was originally conceived to consist of 77 satellites, hence the name Iridium which is 77 on the periodic table of elements. However, the original launch was completed with a total of 66 cross-linked satellites orbiting at a distance of 780 km from the surface of the Earth and services began on November 1, 1998.
In early 2019, Iridium completed a major overhaul of its network by replacing all its satellites and upgrading the supporting ground infrastructure. This enabled the launch of Iridium Certus, a new multi-service platform delivering specialty broadband services, with additional midband services coming soon.  
Iridium: Ten Things to Know About Iridium Certus