means The science and engineering of building or manipulating materials and devices at the scale of atoms and molecules, typically under 100 nanometers.

from A modern compound bolted together from Greek 'nanos' (dwarf) and 'technology' (from 'tekhne,' craft or skill). The 'nano-' prefix was adopted as the metric term for one-billionth, so a nanometer is a billionth of a meter — small enough that a human hair is roughly 80,000 of them wide. The vision was famously seeded mid-20th century by physicist Richard Feynman, who mused there was 'plenty of room at the bottom,' and the word itself was popularized in the late 20th century as the dream of atom-by-atom construction took hold.