Basically, reclamation is to create new land thus increasing the area of a country by filling the sea into riverbeds with sand, also known as landfilling.
The creation of land requires a large amount of work and is costly too. Materials such as sand and mud have to be imported from other countries, mostly from Malaysia and Indonesia.
Singapore has increased 20% of it's original land but more work must be done to create more space for development purposes. Some of this land are used for facilities such as MRTs, and commercial and industrial activities.