Changing Temperature, Changing Density. Most matter increases in volume when it gets hotter. For example, if an iron rod is heated, it will get longer and fatter and its density will decrease. This happens because the mass of the rod stays the same, but its volume increases. The increase in the volume of matter with increasing temperature is called expansion. When cooled down, most matter decreases in volume and increases in density. This decrease in volume is called contraction.
USB-C also builds on the new USB 3.1 standard so to all intents and purposes is the connection type that brings in the new power and speed advantages of USB 3.1. USB-C is still backwards compatible with existing USB variants, but that of course requires adapters.
The USB 2.0 interface can be a limit due to signalling and command overhead as well as spacing between packets. I have a fast SSD connected by USB 2.0. The drive is much faster than the interface (by more a factor of 10). Read Speed maxes out around 33 MB/s and Write Speed at 17.5 MB/s. Write Speeds are almost 50% slower due to a verify-read after the write and the fact that the USB signal is half-duplex as another answer mentions.