From MarineSpecies Introduced Traits Wiki
Definition of Tombolo:
(1) Coastal formation of beach material developed by refraction, diffraction and longshore drift to form a 'neck' connecting a coast to an offshore island or breakwater; or
(2) A causeway-like accretion
spit that connects an offshore rock or island to the main shore, or to another island.
This is the common definition for Tombolo, other definitions can be discussed in the article