My apologies for not being clear.  The term "offshore" has no precise
meaning - one cannot say that the offshore zone starts at such an such a
depth or a specific distance from land: it is a general term only.
That said, in general the ocean can be divided into several zones, which
are not mutually exclusive: the nearshore zone includes the Infratidal
zone, for example, and extreme spring tides can expose the upper portion
of the subtidal zone.

Inter-tidal:   between the upper and lower limits of the tides.

Infratidal/Subtidal:  oceanographers consider the infratidal zone to be
defined as that area of nearshore water column and bottom that is
completely subtidal, but influenced by tidal currents.

Nearshore:  the zone that can be easily fished by small boats that do
not go very far from port - generally within  15 km of the shoreline.

Offshore:  the zone not generally safe to travel  by inshore fishing
vessals - no set definition, but  it is beyond 10 to 15 km for certain,
and is usually correspondingly deep, except over offshore shoals or
shallow seamounts.

abyssal:  very deep water, beyond the continental rise.

Back to work,
Ross M.