Path of Exile is, in part, a game about comparing items. As we progress our character builds into the endgame and continue specializing our skill setups, stat and gear needs become more specific. Most melee characters won't need to bother with spell damage; DoT builds might skip over critical hit chance. Gradually, more and more items become irrelevant, unless they're providing—or can be made to provide—the narrowing set of modifiers a build relies on. With how much loot PoE throws at you, however, weighing the stats of every individual drop would leave you spending more time assessing items than actually playing the game.
Enter the loot filter. Back in 2015, Grinding Gear Games added built-in functionality to filter what items are displayed and highlighted as they tumble out of the countless thousands of slain goatfolk, helping players quickly identify useful items before they've even picked them up. Making your own loot filter can be an involved process, so a cottage industry of loot filter designers emerged, offering bespoke filters for players to install that highlight and emphasize the gear and currency drops that matter most.
As it stands, the initial PoE 2 filter doesn't yet do much automatic gear filtering based on item type and modifiers. For the moment its main utility is highlighting crucial drops like currency, jewelry, and character progression items—as well as socketed and superior-quality gear—with sounds, visible light beams, and varying font sizes, to ensure you don't leave an area while there's an orb still lying on the ground. Can you imagine? Leaving an orb? Awful stuff.
