●In Astronomy, Optics & Photography:
A
which
the
of the
through one
in an
system.
The
of such a
which
the
of the
through the whole system. For a
, this is the
of the
lens.
●In Communication & Space:
The (typically) large-diameter
used for
and
energy
the
used in communication
, especially in the
. For a
, this is
a large
; sometimes called an array.