There are 4 types of visual representation in game UI design: diegetic, non-diegetic, spatial and meta. Diegetic UI elements are seen or heard by the character and fit within the story‘s context. Non-diegetic elements exist outside of the game or story and only the player sees them. Spatial elements are represented within the game space but not visible to characters. Meta elements are contextual to the game but not represented in the game space. It‘s important to understand the meaning and use of these types.
Non-diegetic
Non-diegetic UI components are those that do not exist within the story or space of a game. These components are only seen by the player and not by any of the characters in the game. The design, placement and context of these components are critical for a good player experience. Examples of non-diegetic components in video games are stat meters that track points, time, damage, and resources.
Diegetic
Diegetic UI elements are those that exist both within a game‘s story and space, and are known by the characters in the game, including the player‘s avatar. A challenge in using diegetic components is in scaling, as a small component like an in-game speedometer may not be easily visible.
Spatial
Spatial UI elements are located in the game space but characters in the game don‘t see them. They often act as visual aids to help players select objects or point out landmarks.
Meta
Meta UI components exist in the game‘s story but not in the game space. They can be subtle, like a layer of dirt accumulating on a 2D plane, or they can be prominent like shaking, blurring, or discoloring of the field of view to show player damage.
https://www.toptal.com/designers/gui/game-ui#: UI Components in Games https://www.sketch.com/blog/game-ui-design/: UI Components in Games