It’s a Cabin Hook..

Cabin Hook Noun

Definition of CABIN HOOK

: a small hook and eye for use on cabinet doors

First Known Use of Cabin Hook 1845

Source http://www.merriam-webster.com com/dictionary/cabin%20hook…

They are also used to hold outward opening doors (for example patio doors) against a wall (to stop the doors blowing closed in a strong wind) when there is no rain.

Can be used to secure the doors to boats.

Some examples:

An example on an in a boat: