Michigan
A strip of water between two land masses is called a strait.
Michigan is composed of two unconnected land masses, the Upper Peninsula and the Lower Peninsula. They are separated by the Straits of Mackinac, where the Mackinac Bridge spans the gap.
Michigan is the only state made of two separate land masses.
The Upper Peninsula of Michigan is the northern of the two major land masses and the cold water.
Isthmus
It is called a strait.
It is called an isthmus.
Michigan is composed of two unconnected peninsulas...probably the answer you are looking for. Part of Fulton County, Kentucky is completely surrounded by Missouri and Tennessee and unconnected from the rest of the state. So, Kentucky is actually composed of two unconnected pieces of land...probably wouldn't be considered a "land mass" though...
isthmus
a narror stip of land that joins two land masses and separates two water bodies is called an isthumus
Land bridge.