For many people that question is best answered by saying
that it is the collapsed crystal structure of the solid state.
The small blocks of collapsed solid are free to move around,
passing over one another. This explains the concept of fluidity.
For other people, the concept of the liquid state is best
explained with the
Flickering Cluster Theory.
That is the approach that will be
taken here. However, remember, regardless of the name, most descriptions
of the liquid state are basically the same. They will only differ
in some of the details.