A seascape is a photograph, painting, or other work of art which depicts the sea, in other words an example of marine art. By a backwards development, the word has also come to mean the view of the sea itself, and be applied in planning contexts to geographical locations possessing a good view of the sea.
In the UK a seascape is defined in planning and land use contexts as a combination of adjacent land, coastline and sea within an area, defined by a mix of land-sea inter-visibility and coastal landscape character assessment, with major headlands forming division points between one seascape area and the next. This approach to coastal landscape planning was developed jointly by Government environmental bodies in Wales (UK) and Ireland in 2000 to assist spatial planning for (at that time new) offshore wind farm developments. The resulting "Guide to best practice in seascape assessment ", (Marine Institute, Ireland, 2001), have since been adapted and applied in Scotland  and Wales for guidance to offshore wind farm developers and for carrying out spatial planning assessments.
Meanwhile the word has also been adopted in England referring to the historic and archaeological character areas of the sea - a different but complementary methodological approach encompassing what lies beneath the sea surface. This use of the word departs from the focus on scenery and visual perception, relying instead just on cognitive perception (what lies beneath the sea surface is out of sight to most of us).
The Welsh language already distinguishes between 'Morluniau' (seascape in the traditional sense of a picture, view or painting) and 'Morweddau' (seascape as a distinct, geographical area exhibiting particular characteristics and qualities). There is no such distinction in the English language.