Yes, i should have said mini/micro to cover all my bases. It doesn't matter because i was simply referring to non-full-size ports. As to OTG, you need to study up on what that actually is. OTG is a protocol stacked on top of the standard USB Protocol. You see, normally USB devices operate in a host-client relationship. Meaning, there are USB-capable devices that act as hosts (PCs to give one prominent example) and are unable to function as a client (the reason why you can't connect two computers with a USB cable). Then there are devices that function as clients (usb drives, media players, usb peripherals, etc.) and are unable to function as hosts ( the reason why you can't connect two mp3 players with a USB cable and transfer data between them). You have to have a host on one end and a client on the other. That's how it works.
USB OTG, on the other hand, is an additional protocol that allows a device to act either as a client or as a host. That's what enables you to plug a usb mouse, keyboard, flash drive, etc. into your phone and be able to use it, because the phone is set up to act as the host. It just so happens that the USB consortium have set a requirement for only mini-A or mini-B usb connections ( their words, not mine) to be used on OTG capable devices. So although a micro-usb to USB-A adapter or a USB-C to USB-A adapter may be called OTG adapters, OTG really signifies the capabilities of the devices being used with the adapters, not the adapters themselves.