The full form of OML is Oh My God
OML stands for “Oh, My Lord” and is similar to OMG, standing for “Oh My God”. OML is used just like OMG when one wishes to express disbelief or excitement. Therefore, OML can be used both in a negative or positive light depending on the circumstance.

Origin of OML

Exclaiming the name of God or the Lord, despite always being considered a bad thing in most religions, has for centuries been used to express disdain or excitement. When internet and text messaging became popular in the 1980s and 1990s, using either OMG or OML became common. While not as common as OMG, OML still sees usage and is viewed in a humorous light, usually aping elderly religious persons who are likely to use “Oh my Lord” or possibly “Lordy”.

Other Meanings
Because it is an acronym, OML has two other uses. The first is for “Oh, My Life”. This is to express disdain for something negative that is occurring like a break-up or receiving a poor grade. The second usage is “On My Life”. This is used as a swear of promise. Using OML for “On My Life” means what you are saying is indeed true and you aren’t lying.