If its been properly reclaimed, usually.
Land reclaimed from the sea is often referred to as reclamation land or land reclamation. It involves altering coastlines or waterways to create new land for various purposes such as urban development or agriculture.
in the Netherlands we call reclaimed land "polders"
polder
They reclaimed it from the North Sea, not land.
Yes
Examples: Parts of Tuas are on reclaimed land. Jurong Island used to be two separate islands. The land between the islands was reclaimed to fuse them together.
Lands reclaimed by the sea can be called either land fills or reclamation ground. In New Zealand, it is called land rehabilitation.
It is Kansai Airport.
ondergelopen grond
I don't really know what 'land that was reclaimed' you mean, there are multiple areas where first was water and now is land. But if you mean "de Zuiderzee", there where first was sea and now is land (the biggest area that was reclaimed): The Dutch build a big dike (called "de Afsluitdijk"), making "de Zuiderzee" a lake and no longer a part of the sea. This lake, which was and still is called "het IJsselmeer" isn't completely made into land however, only some of the southern parts and some other smaller parts around the lake. These southern parts of the former "Zuiderzee" that now lie there are called "Flevoland" and the "Noordoostpolder". And if you simply mean how any reclaimed land would be called in the Netherlands, they usually call it a polder. I hope this answers the question.
Land is being reclaimed from the sea.