Imagine being able to observe the motion of a red blood cell as it moves through your vein, or being able to watch as a type of white blood cell (called a "T-cell") destroys an invading microbe by engulfing it. What would it be like to observe the vibration of molecules as the temperature rises in a pan of water? To observe sodium and chlorine atoms as they get close enough to actually transfer electrons and form a salt crystal? New scientific tools, developed and improved over the last few decades, make such observations increasingly feasible. These are examples of the effort to view, measure and even manipulate materials at the molecular or atomic scale - the major focus of nanotechnology.
The prefix "nano" comes from a Greek word, νᾶνος, that means "dwarf". This prefix is used in the International System of Units (SI) to denote a factor of 10−9. If we have the "nano" prefix attached to a meter (m) then 1 nm (nanometer) = 10−9 meter (one billinoth of a meter, according to the "short scale" definition of a billion used in English-speaking countries). If the prefix is attached to a second (sec) then 1 ns =10−9 second (1 biilionth of a second).
Three dimensional view of an AFM image of a Aluminum gate single-wall Carbon nanotube (SWCNT) Field Effect Transistor (FET). Image source: MSU Nanomanufacturing Lab
Most quantities involving "nano" are considered "very small."
Individual atoms are smaller than 1 nm (1 nanometer) in diameter. It takes about 10 hydrogen atoms arranged in a row to create a line 1 nm in length. Other atoms are larger than hydrogen, but still have diameters less than 1 nm. A typical virus is about 100 nm in diameter and a bacterium is about 1000 nm head to tail.