If you are a fan of Raspberry Pi Zero series of Single Board Computer, you will know that it does not come with proper USB socket for USB devices. There is only USB micro B connectors. But to start using Raspberry Pi Zero, you will most likely need a USB keyboard (at minimum), so this is where the USB OTG adapter cable come in.
This is official Raspberry Pi micro USB OTG adapter cable. This cable looks like a USB micro cable but it isn't! Instead of a USB A Plug, it has a USB A Socket on the end. This cable is designed for use with OTG (On the Go) host devices (like the Arduino Due or many tablets) so you can connect a mouse, keyboard, or any other USB device to the host via this cable.
For the Raspberry Pi Zero case, this adapter enable the Zero to use USB keyboard or mouse, or you can connect a USB hub to connect more USB devices. Compatible with: