Wetlands are areas that are totally or partially covered with water. They are transitional between permanently flooded deep water areas and areas with their water tables near the surface. Sometimes, shallow water covers the surface of the land. Examples of wetlands are:

brackish marsh,
fresh marshes,
salt marshes,
swamps,
wet prairies,
bogs,
forested wetlands,
and vernal pools. 
You can also refer to wetlands as areas with dominant natural water saturation levels, determining the soil development processes and the plants and animals inhabiting them. The covering of water in some wetlands could be permanent or seasonal.

Inland wetlands develop in isolated depressions surrounded by dry land. An inland wetland's soil is very poorly drained, often found in floodplains or other areas prone to flooding. The various inland wetlands are:

Inland and coastal wetlands can remove carbon and other greenhouse gases from the atmosphere and transfer them into the wetlands’ soil as organic soil matter. Wetland producers remove carbon dioxide through photosynthesis2. Then, they convert it into cellulose and other carbon compounds before it becomes soil organic matter.