What is USB?
There are a lot of types od USB ports, here are only some of them:
Released in January 1996, USB 1.0 specified data rates of 1.5 Mbit/s (Low-Bandwidth) and 12 Mbit/s (Full-Bandwidth). It did not allow for extension cables or pass-through monitors, due to timing and power limitations.
USB 2.0 was released in April 2000 (now called "Hi-Speed"), adding higher maximum signaling rate of 480 Mbit/s (due to bus access constraints the effective throughput is limited to 35 MB/s or 280 Mbit/s), in addition to the "USB 1.x Full Speed" signaling rate of 12 Mbit/s.
USB 3.0 was released in November 2008. The standard defines a new SuperSpeed mode with a signaling speed of 5 Gbit/s and, due to encoding overhead, usable data rate of up to 4 Gbit/s (500 MB/s). A USB 3.0 port is usually colored blue, and is backwards compatible with USB 2.0.