I am not a teacher.
It's a way of expressing a distance out to sea, measured from the coast.

Interested in Language
I quoted a original sentences from CNN news site,
What does "off" mean in this sentence?
Much of what is imported to Chad comes through the Cameroonian seaport of Douala, and Chad's crude oil is transported through a pipeline that runs from southern Chad to a floating facility 11 kilometers (almost 7 miles) off the Cameroon coast.
I am not a teacher.
It's a way of expressing a distance out to sea, measured from the coast.
I take 'off' to mean 'away from', according to http://www.ldoceonline.com/dictionary/off_1
Not a teacher.
Or simply 'from'.
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