The term "hardon" refers to the physical act or result of a man's penis becoming erect, also known as an erection. In the context of porn video tags, this term is used to indicate that a particular scene or content involves a man having an erection, which is typically a key aspect of sexual activities depicted in adult films. An erection occurs when blood flows into the spongy tissue of the penis, causing it to become firm and rigid. This is often a sign of sexual arousal and attraction in men.