The so-called 5 Gb/s USB has a data rate of 4 Gb/s.
The marketing data rates for Ethernet are true, i.e. 1 Gb/s Ethernet has a 1 Gb/s data rate, but a 1.25 Gb/s encoded bit rate over the cable.
The marketing data rates for the first 2 generations of PCIe, for all 3 generations of SATA, and for USB 3.0 a.k.a. "Gen 1" of later standards, are false, being advertised as larger with 25% (because 8 data bits are encoded into 10 bits sent over the wire, which does not matter for the user).
All these misleading marketing data rates have been introduced by Intel, who did not follow the rules used in vendor-neutral standards, like Ethernet.
So PCIe 1 is 2 Gb/s, PCIe 2 & USB 3.0 are 4 Gb/s and SATA 3 is 4.8 Gb/s.
So USB "5 Gbps" => 500 MB/s (not 625 MB/s), and after accounting for protocols like "USB Attached SCSI Protocol", the maximum speed that one can see for an USB SSD on a "5 Gbps" port is between 400 MB/s and 450 MB/s.
The same applies for a USB Type C with 2 x 5 Gb/s links.
As other posters have already mentioned, USB 3.1 a.k.a. the "Gen 2" of later standards has introduced a more efficient encoding, so its speed is approximately 10 Gb/s.
The "10 Gbps" USB is not twice faster than the "5 Gbps" USB, it is 2.5 times faster, and this is important to know.