USB-C, formally known as USB Type-C, is a 24-pin USB connector system, which is distinguished by its almost two-fold rotationally-symmetrical connector. (Symmetry is broken, typically by a seam in the outer metal mating surface)
The USB Type-C Specification 1.0 was published by the USB Implementers Forum (USB-IF) and was finalized in August 2014. It was developed at roughly the same time as the USB 3.1 specification. In July 2016, it was adopted by the IEC as “IEC 62680-1-3”.
A device with a Type-C connector does not necessarily implement USB, USB Power Delivery, or any Alternate Mode: the Type-C connector is common to several technologies while mandating only a few of them.
USB 3.2, released in September 2017, replaces the USB 3.1 standard. It preserves existing USB 3.1 SuperSpeed and SuperSpeed+ data modes and introduces two new SuperSpeed+ transfer modes over the USB-C connector using two-lane operation, with data rates of 10 and 20 Gbit/s (1 and ~2.4 GB/s).
USB4 released in 2019 is the first USB transfer protocol standard that is only available via USB-C.