What is this type of wiring?

[esarratt]

I was looking at LEDs today and one of the lights was pre-wired with 3 Feet of 16/3-SO Cable.

I know this is 3-strand 16 gauge and the "S" probably stands for shielded, but what about the O. I have Googled and Googled to no avail.

I have found an SOOW, but no SO.

Any marine electricians or knowledgeable parties please speak up.

Thanks.

[beneteau-500]

SO = s service cable up to 600 v o is oil resistant outer sheeve

[esarratt]

Thanks!