The very small USB port found on many non-Apple cellphones, tablets and other portable devices is a Micro USB socket. Considerably smaller than USB Type A and B, Micro USB is also half the thickness of Mini USB (see illustration below). Micro USB has been superseded by USB Type C on many new products. See Mini USB
, USB Type C
, USB 3.0
, USB OTG
The Smallest USB Socket
The cable that plugs into the Micro USB 2.0 socket on this smartphone has a Type A plug at the other end for the computer or AC charger. Micro USB 3.0 sockets accept a 2.0 plug, but not vice versa.
Micro USB 2.0 and 3.0
These are the two Micro-B sockets. A 5-pin USB 2.0 plug will slide into the left side of a 10-pin 3.0 socket but obviously not the other way around.
Two-in-One Micro USB/USB
The common USB Type A and Micro-B can be combined in the same plug by using a moving outer shell.