Term for Internet or Texting Acronyms, e.g. LOL, IMHO, M8

What are the acronym, internet words like lol, brb, imho, etc., called? Is there such a term beyond acronym? I was wanting to tell someone that someone else was not familiar with the meme/internet jargon/acronym 'M8' (or mate), but couldn't think of a reasonable word to use.

So, is there a term that would define these terms for how they are different than other, regular english 'SMS text'. Moreover, we find these terms more and more in the wild and not necessarily even on electronic devices, like on t-shirts or even spoken.

If I e-mail the message, "I'll be leaving the office at 10, but then I'll brb." What would I call the 'brb' part of the message, apart from the rest? "He e-mailed his boss a message saying 'He'd be right back', but he decided using an [internet jargon] was acceptable."

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Update 02/01/2018

Although I have accepted an answer for now, I think it is inadequate, and that a word will eventually be coined to define these text terms. Until then...

Answer

Generally, it's called "chat speak" or "text speak" as it originated in shorthand used when writing text messages and in chat rooms on the internet.

The main Wikipedia article calls it SMS language but I've never heard that term before.

SMS language or textese (also known as txt-speak, txtese, chatspeak, txt, txtspk, txtk, txto, texting language, txt lingo, SMSish, txtslang, txt talk) is a term for the abbreviations and slang commonly used with mobile phone text messaging, but sometimes used with other Internet-based communication such as email and instant messaging.

The Wikipedia article includes lists of examples that include the ones you've listed in your question.

Another source of information, NetLingo.com broadens the terms for this to include:

a.k.a. Internet acronyms, text message jargon, abbreviations, initialisms, cyberslang, leetspeak, SMS code, textese

Note that leetspeak (or just leet) is generally considered a separate entity from chat/text speak, as it uses more numerals and special suffixes and also encompasses things like ASCII art.

LOL, notably, has its own Wikipedia article where it is defined as being internet slang:

LOL or lol, an acronym for laugh(ing) out loud, or lots of laughs, is a popular element of Internet slang. It was first used almost exclusively on Usenet, but has since become widespread in other forms of computer-mediated communication and even face-to-face communication. It is one of many initialisms for expressing bodily reactions, in particular laughter, as text, including initialisms for more emphatic expressions of laughter such as LMAO ("laugh(ing) my ass off") and ROFL (or its older form ROTFL; "roll(ing) on the floor laughing"). Other unrelated expansions include the now mostly obsolete "lots of luck" or "lots of love" used in letter-writing.