https://phys.org/news/2018-06-elon-musk-wrong-nanotechnology.html

So is nanotech just a buzzword used to jazz up some otherwise dull research? Or is it a real branch of scientific discovery that's actually making a difference to the world?

Nano means small, really small. One nanometre is just one billionth of metre. At this scale we're dealing with individual molecules and atoms (a carbon atom is about 0.3 nanometres across). So nanotech is about arranging matter that's between one nanometre and 100 nanometres across in at least one dimension, to create usable medicines, electronics and materials.