Final answer:
A natural sand bar or low sand ridge that connects one island to another or to the mainland is called a tombolo, often found in coastal environments next to bays or lagoons.
Step-by-step explanation:
A natural sand bar or low, sand ridge that connects one island to another island or to the mainland is called a tombolo. A tombolo is formed by the deposition of sand and other sediments, which can create a land bridge between two landmasses. These formations are often found in coastal environments and can be associated with features such as a bay or lagoon, which is an area of relatively shallow water that may sport high salinity and significant tides, and is often separated from the open sea by a natural barrier like a sand spit, barrier island, or coral reef.