Its the most recent industry-standard USB post specification, which aims to finally solve the wired computer interfacing. USB-C is a very versatile connector that supports very fast data transfer and power delivery. The 2016 MBPs implement Thunderbolt3 via USB-C connector, which allows them to support daisy-chainable storage devices or displays with very high speed. At the same time, the USB-C port supports the USB3.1 data transfer interface (10Gb/s), video out, 100W power delivery and many other things.
In short: its a port that serves as your high-speed data port, charging port, ethernet port, external display port, whatever port, and its industry standard on top of it. Right now, its still a relative novelty, but every new laptop is now adopting it and the number of existing peripheral devices is raising quickly. In a short while, when the market is more filled with useful stuff, you could for example do things like use a single-port dock to charge your MBP and connect it to all the devices on your desk. Or use third-party external batteries/battery packs. And so on.