What is a 'nanoparticle'?

A Nanoparticle
A nanoparticle is unit that has a width ranging from a few nanometers (nm) to a couple of hundred. What is different about using particles at this size is because the properties of materials change as their size approaches the nanoscale.

The reason why these Nanoparticles are currently under intense scientific interest is because of the extensive possiblity for these tiny units to be used in a wide range of applications.