Dear Ch. V. Ramana Murthy ,

If you look for the definition of "nanofluid", you will find the following:

A nanofluid is a fluid containing nanometer-sized particles, called nanoparticles.

The main aspect that you should accomplish to consider a fluid as a "nanofluid" is that the filler in that fluid should have nanometer size (being 1 nm = 10e-9 m). In a more general case, a nanofluid can have 2 liquid phases, in which one of the phases is distributed in nanosized droplets too.

Hope this helps!