A spit is a land form found off coasts. It forms when sediment builds up and a landmass is left. The sediment is deposited by waves. This is called longshore drift. When a spit forms, one end remains connected to the land while the other end exists in open water.
A salt marsh is "an environment between land and salty or brakish water, dominated by dense stands of salt-tolerant plants such as herbs, grasses or low shrubs." Salt marshes occur on low-energy coasts in temperate climates and high-latitudes.
A mudflat (aka tidal flats) is a coastal wetland that forms when mud is deposited by tides or rivers. "Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine animal detritus.