Nanotechnology was a field of science and technology involving devices so small that the naked eye could not see them.
Denobulans were known to have experimented with nanotechnology by the early 2150s. (ENT: "Regeneration")
The Borg Collective was infamous for their use of nanotechnology to advance their goals, specifically assimilating new members and technologies with nanoprobes. (VOY: "Scorpion")
The Federation Starfleet also commonly used nanotechnology, such as in isolinear circuitry. In 2366, Wesley Crusher was experimenting with nanites, small robotic devices in the field of nanotechnology. (TNG: "Evolution")
Major Kira Nerys once delayed Vedek Winn's ship and claimed it was to inspect for nanotechnology. (DS9: "The Collaborator")