HD here refers to picture resolution, typically 720p or above. It points to the technical side of a video file rather than anything about the men on screen or what happens between them. Terms that sit alongside it in this niche, such as anal, blowjob or bareback, describe activity or conditions, while bareback specifically concerns the absence of a condom. So a resolution tag and a content tag answer two different questions: how sharp the footage looks, and what the footage is about.