Yunk in the context of Steemit is a nonsense word that originated in general chat - steemit.chat

It's use began shortly after @yunkzilla began his witness campaign and is now a dedicated channel in Steemit chat and has become a trending tag for posts. The tag is utilised by members of general chat to easily identify & curate the posts of other chat users & to promote @yunkzilla's witness campaign efforts.

I hope that this has answered your question.