Apparently this originated from someone's 2017 Inktober Prompt list: https://semmyjart.tumblr.com/post/165449654676/im-going-to-participate-in-inktober-this-year-but
26 Sep 2018
"OC" standing for "Original Character" here. This is a drawing challenge running annually throughout September
What's the challenge? Draw your OCs, ideally one image per day.
Where, how to take part: Post anywhere using the tag "oc-tober".