Definiton of "Davey Jone's locker"?

[Zishuli]

English Language Tests, Intermediate level

ESL/EFL Test #329 "English Slang Idioms (50)", question 8

"We have to find a new captain. The ship went down and its captain is in Davey Jones' .........," the commodore told the admiral.

(a) caboose
(b) dungeon
(c) locker
(d) treasure

English Language Tests, Intermediate level

ESL/EFL Test #329 "English Slang Idioms (50)", answer 8

"We have to find a new captain. The ship went down and its captain is in Davey Jones' locker," the commodore told the admiral.

Correct answer: (c) locker
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Hi,
I have looked up the dictionary but I failed to find out the definiton of "Davey Jone's locker". Can anyone help me?

[Mister Micawber]

.
The ocean, especially as a place where sailors are lost or drown.
.
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Native English teacher at Mister Micawber's