what is the difinetion of eclipse in virology?

Answer 1

It's the phase of viral replication where the viral particles can not be reconginzed by the host's immune system.

Answer 2

It's a little different for different viruses, but basically the eclipse phase is when there are no infectious virions to be found either inside or outside the host cell. This occurs just after viral entry, and is sometimes associated with viral takeover of the host machinery.