BTW - By the way
SWMBO - She who must be obeyed
IMHO - In my humble opinion
<G> - Grin
<BG> - Big Grin
LOL - Laugh out Loud
ROFL - Roll on Floor Laughing
LFMHO - Laughed my f**king head off
JFRO - Just f**k right off
Not forgetting TIA (thanks in advance) or RTM (read the manual - sometimes expressed more frustradely as RTFM).
But were you thinking about TLA (three letter acronyms) like COG (course over ground), SOG (speed over ground), ETA (estimated time of arrival), XTE (cross track error), CTS (course to steer), MOB (man overboard position)?
Then of course there are the time honoured LOA (length over all), LWL (length waterline), BMAX (maximum beam), DNS (did not start), DNF (did not finish), DSQ (disqualified), LAT (lowest astronomical tide), LWS, LWN, HWS, HWN (high and low water, springs and neaps), UTC (universal time), ETC (etcetera).
NM=No Message. It means that the answer or contribution is encapsulated in the title of the post, and no need for any text. To make the software work, you have to puttin a bit of text, so some people put in a full stop or an x or whatever
Systeme Internationale. Or Standard Internationale? - I've been barred from using search engines and then posting hereabouts! Believe that there used to be a long piece of metal in Paris that you could check, but now it's based on the wavelength of light erm from something.