Imagine something so small that it’s a million times smaller than the length of an ant. Then consider the ability to manipulate something that small to solve problems and create new products. Welcome to the world of nanotechnology.
Nanotechnology is the understanding, manipulation, and control of matter at dimensions of roughly 1 to 100 nanometers, which is near-atomic scale, to produce new materials, devices, and structures. One nanometer is one-billionth of a meter. Putting this size into perspective, a single human hair is about 80,000 nanometers in width and a red blood cell is about 7,000 nanometers in diameter.
One nanometer (nm) is one billionth, or 10−9, of a meter. By comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12–0.15 nm, and a DNA double-helix has a diameter around 2 nm. On the other hand, the smallest cellular life-forms, the bacteria of the genus Mycoplasma, are around 200 nm in length. By convention, nanotechnology is taken as the scale range 1 to 100 nm following the definition used by the National Nanotechnology Initiative in the US. The lower limit is set by the size of atoms (hydrogen has the smallest atoms, which are approximately a quarter of a nm diameter) since nanotechnology must build its devices from atoms and molecules. The upper limit is more or less arbitrary but is around the size below which phenomena not observed in larger structures start to become apparent and can be made use of in the nano device. These new phenomena make nanotechnology distinct from devices which are merely miniaturized versions of an equivalent macroscopic device; such devices are on a larger scale and come under the description of microtechnology.
To put that scale in another context, the comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth.  Or another way of putting it: a nanometer is the amount an average man’s beard grows in the time it takes him to raise the razor to his face.