While technically "HD," these are often marketed as UHD (Ultra High Definition). Many modern searches for mp4hdmovies actually intend to find 4K content, though true 4K MP4 files can be massive (20GB+). The H.265 (HEVC) codec is essential here to keep file sizes practical.
When we talk about mp4hdmovies, we must clarify the different tiers of "High Definition." Not all HD is created equal.
You do not have to break the law to enjoy this format. Many legitimate services provide legal downloads of MP4 files.