The term "cock-wank" is slang for a specific sexual activity involving masturbation. In English, it means that the scene or content involves a person (usually a man) manually stimulating their own penis, also known as masturbation. This act can be performed with or without lubricants, and may lead to ejaculation. The term "cock" is a colloquial term for a male's genitals, while "wank" is British slang for masturbation.
In the context of porn videos, this tag would indicate that the video contains scenes where men are pleasuring themselves by manually stimulating their genitals. It might also suggest a solo or self-pleasure type of video without any other partners involved.