OMT is a variation of OMG meaning "Oh My Toph
It was created when a fan of the hit show Avatar: The Last Airbender
no longer found "OMG
", or "Oh My God", a suitable acronym to describe events occurring in the show, half because the show required a more fitting letter and half because the fan didn't like using the Lord's name in vain.
And because Toph is one of the most kickass characters, the G was substituted with a T to represent the general awesomeness of Toph.
The term was first used in conversation between two fan fiction writers, but spread once the duo began a livejournal community called CAPSLOCK_TOKKA
Afterwards, as the term became more well-known, it spread to various other websites related to Avatar, including ASN and KF.net.