Acronyms: A word (as NATO, or FBI) formed from the initial letter or letters of each of the successive parts or major parts of a compound term. See Merriam-Webster.
* BTW: By The Way.
* FYI: For Your Information. FYI often means that a response isn't expected. An the primary purpose of FYI is to indicate that it's something of low importance.
* NRN: No Response Needed. Sometimes, without body language, it isn't clear when an email-based conversation should be ended.
* IMHO: In My Humble, or Honest Opinion.
* RTFM: Read The Manual ("Manual" here refers to any documentation).
* LOL: [I] Laughed Out Loud (at what you wrote).
* ROTFL: [I am] Rolling On The Floor Laughing (at what you wrote).
* RSN: Real Soon Now
* TIA: Thanks In Advance.
Of course, there are others. You can add them. Welcome.