USB OTG is expanded for Universal Serial Bus – On The Go, This is a function from which an USB device can be connected to phone, music player or any other embedded device. Usually phones are connected to personal computers as clients but by using OTG connectivity the mobile phone can be turned into a host upon which other devices can be connected as clients to phone using an OTG cable. Which usually comes in two or three different forms. To know which version to choose from for your phone, refer this article -> OTG troubleshooting .
Before that, let us see what is OTG and what are all the things we can do with it. As we discussed in the above sentence, OTG is a connectivity function. To see in brief, let us take flash drive as an example, which is also one of the major device to be accessed using OTG. Usually pendrives can be accessed from personal computers, But to connect it to phone using OTG one must need a cable which is compatible for phone’s microUSB as well as the pendrives standard size USB. So that the files on the flash drive can be accessible and editable on phone.
More applications are being invented to use OTG, Some of the important ones are: Connecting two phones and creating a wired network, just like wifi hotspot feature, Connecting phones to networks using Ethernet.
To know more about OTG cables check out our detailed article on using OTGs -> How to use OTG cable
More reference : USB wiki