An atmospheric (or "atmo" for short) item is one that periodically emits messaging to the entire room without any action on the player's part. Common examples include Planetary Gems, certain forehead gems, "floaters"/"drifters," snake charms, flower charms, bird charms, and "shimmer" garments.
The terms "atmospheric item" and "atmo item" are often regarded as OOC. A more IC alternative is to describe what the item is doing, such as "animated," "flashy," "shimmering," or "noisy" (if the item makes noise).
To reduce scroll and/or lag during major events, common etiquette is to turn off atmospheric items. This can be done by either removing the item or by holding it and using the Atmosphere command.
Many players regard atmospheric item messaging as unnecessary spam. When several players in a crowd are wearing such items, the screen can scroll by very quickly, making it more difficult to follow events. To mitigate this issue, GMs have been working to route all atmospheric item messaging to the Atmospherics window instead of the game window. (Depending on settings, this may completely remove such messaging from the game window.)
If you see an atmospheric item that is not being sent to the Atmospherics window, please use the Bug command to report it. If you are not holding the item, include the messaging that you see so that GMs can figure out which item you're reporting.
In extreme cases, the use of atmospheric items can cause game-wide lag and/or instability. For example, during the Hollow Eve Festival 414 Auction, which had dozens of players in the same room, the game did not stop crashing until those who were attending the auction turned off their atmospheric items and stopped teaching classes.