The term usually refers to a third-party application (often an APK for Android devices, Firestick, or PC) that aggregates streaming links for movies and TV shows. The "3" likely signifies a version number or a specific clone/fork of a popular app (similar to how there are many "Cinema HD" clones).
Perhaps you already have a media player (like Windows Media Player 12), but it refuses to play modern HD files. In that case, an hd movie 3 install means installing a codec pack. hd movie 3 install
If you manage to install a working version of the app, here is what the experience is typically like: The term usually refers to a third-party application
Initial settings to adjust:
Typical red flags:
Action plan: