What does Cloverfield mean?

Answer 1

Its a name of a street, it was a fake name for the movie but because of its popularity it stuck. It may be the government's call sign for a monster attack.

It could also mean nothing.

One theory: In instances where poor soil conditions exist (such as the state of Manhattan at the end of the film) clover is the only thing which can grow, as it takes nitrogen from the air and not the soil. Thus, Manhattan would essentially become a clover field.