The phrase "high def" is a short way of saying "high definition". It means that something is very clear and detailed, usually referring to the quality of images or videos. Full definition
Released here for the first time in high def, the film hasn't shown too much age and is likely the best the film has looked since its original release. (fulvuedrive-in.com)
It also means that when you're taking high def video that the memory card can keep up. (travelblogbreakthrough.com)
These are high def cameras that take beautiful pictures. (geekwrapped.com)