To better understand what we mean about Type C being a replacement for both ends of the cable, you first need to understand the differences between the existing versions of USB and the various Type-A and Type-B connections.
USB versions refer to the overall standard and they define the maximum speed of the connection, the maximum power and much more besides. They theoretically could be applied to any shape of connector so long as the computer and device are connected up correctly.
Although USB 1.0 is technically the first version of USB it never really made it to market so USB 1.1 is the first standard we all used. It could deliver data at 12Mbps and maximum current draw of 100mA.
The second version of USB arrived in April 2000 and it provided a massive boost in maximum data throughput, up to 480Mbps. Power draw was also increased to a maximum of 1.8A at 2.5V.
USB 3.0 was a big change as it brought new connector types to allow for its extra speed and power draw, with them often coloured blue to denote their prowess. USB 3.0 can run at up to 5Gbps, delivering 5V at 1.8A. It arrived in November 2008.
The latest and greatest version of USB was released in July 2013, though uptake is still almost non-existent. It can deliver 10Gbps of throughput while up to 2A can be drawn over 5V, and optionally either 5A over 12V (60W) or 20V (100W). This is the reason the new MacBook can be powered just by its USB connection.