Some are abbreviations, others are acronyms. There can be hundreds of meanings for a single acronym. It depends on the context in which they are used. Some are more common than others. If you are looking at things for sale, OBO means "or best offer", POA, "price on application". ARM usually refers to "adjustable rate mortgage". SUV can mean Sports Utility Vehicle but it can also mean Senseless Urban Vulgarity or Snob's Upperclass Van. Some are frequently used on the internet, IMHO is "in my humble opinion". ROLMAO, "rolling on the ground laughing my ass off", LOML, "love of my life", SWMBO, "she who must be obeyed" . Many others are used in texting over cell phones, if you have teenagers, you might want to get a handle on some of those so you know what they are texting about. 420 refers to smoking pot. PoP, "parents on the prowl". Some may have special codes that they're group only knows. The military is famous for acronyms and that may have been where it got started, SNAFU, FUBAR, BOHICA, you can look those up. Police use number codes on the radio, 10-4, "message received", 10-16, "domestic problem". In woodworking forums, BLO is "boiled linseed oil", RO, "random orbit sander, SCMS, "sliding compound miter saw".