What this stands for depends on whether or not you're 13 years old, or not.
If you're a hobbyist (like myself) who likes
working with printed circuit boards (PCBs), SMD stands for Surface Mount Device, which are devices that are soldered onto the board from only one side, in contrast to THT (Through Hole
Technology) devices.
And if you're a prepubescent 13 year old, I suppose SMD stands for "
suck my dick", just like everyone else who has defined this term thus far on here...