HD can refer to different things depending on the context. Here are some possible meanings:

• High-definition video: HD video is video of higher resolution and quality than standard-definition. While there is no standardized meaning for high-definition, generally any video image with a vertical resolution of 720 pixels or higher can be considered HD. The EU defines HD resolution as 1920 x 1080 pixels or 2,073,600 pixels and UHD resolution as 3840 x 2160 pixels or 8,294,400 pixels.

• Huntingtons disease: Huntingtons disease (HD) is a fatal genetic disorder that causes the progressive breakdown of nerve cells in the brain. It deteriorates a persons physical, mental, and emotional abilities, usually during their prime working years, and currently has no cure. HD is characterized by a triad of symptoms, including progressive motor dysfunction, behavioral disturbance, and cognitive decline. Every child of a parent with HD has a 50/50 chance of inheriting the faulty gene that causes the disease.

• Image resolution: HD can also refer to image resolution. Full HD refers to 1080p image resolution, which is the standard resolution for Blu-Ray, digital television, and most HD videos found online. Below Full HD sits standard high definition or 720p – a high definition image resolution that is lower than full 1080p. On the upper end of the spectrum, there is Ultra HD (UHD or 4K), which is larger, crisper, and clearer than even 1080p. The term "HD Ready," when used to describe a television or monitor, refers to a 720p image resolution.

In summary, HD can refer to high-definition video, Huntingtons disease, or image resolution.