Think of it like this:

* Peninsula: The "finger" pointing out into the water.

* Isthmus: The "wrist" connecting the finger to the hand.

* Larger landmass: The "hand" the finger is attached to.

Some examples of peninsulas include:

* Florida (connected to the rest of the US by the Florida Panhandle)

* Italy (connected to Europe by the Alps)

* Korea (connected to mainland Asia by a narrow isthmus)