A heads-up display (HUD) is a visual information display that provides important information for the player during the course of the video game. Information such as health status, weapon ammunition amount, and more are things that are shown on the HUD.
The HUD is one of the most important aspect and source of in-game information for the player, displaying vital information and data regarding the player's current status. Throughout the Splinter Cell series, the HUD has gone through both subtle and drastic changes throughout the game series. Through all the games, however, some aspects of the HUD have remained through the series: current weapon information (ammo count), current health status and aiming indicator.
In Tom Clancy's Splinter Cell and Splinter Cell: Pandora Tomorrow, the HUD remains very similar to each other (besides a few minor changes). The player's health is represented as a vertical bar on the right side of the screen. Below the bar lies the equipment (weapons/gadget) information, detailing the weapon ammunition count and gadget number. Above the equipment information box is the stealth meter, and above the stealth meter are OPSAT notifications letting the player know if they've received new Goals, Notes or Data, respectively. In the upper right side of the screen sits the communications box, which displays a text readout of ingoing and outgoing dialogue during the mission. The Interaction System is appears in the upper right area of the screen when the player is able to interact with the environment.
In Splinter Cell: Chaos Theory, the HUD remains similar but, like Pandora Tomorrow, has undergone different changes. Now between the stealth meter and the equipment information box sits the sound meter, which indicates the current sound output the player is currently making (additionally, an empty white box tracks environmental noise separately). The health bar is now located in the upper right side of the screen and, instead of vertically, the health bar is now horizontal.
In Splinter Cell: Double Agent (Version 1), the HUD is drastically different from the previous games. For one, the objective bar resides on the left side of the screen and a single colored dot (the stealth meter) is located on the left side of it. The Interaction System is represented by icons now and areas of the HUD (like the weapon/gadget information) is removed from the HUD when it isn't in use.
In Splinter Cell: Conviction and Splinter Cell: Blacklist, the HUD is very minimalist, but the two games share a similar theme of removing HUD information on the screen. Weapon information moved back to the right side of the screen, and in Blacklist, the HUD can be enabled to disappear when it's not in use for a while.