"Item" isn't a standard Magic: The Gathering keyword or ability—it doesn't appear in the comprehensive rules. You may be thinking of a few related concepts that do exist in the game.
The closest official term is Artifact, a card type representing magical or mechanical objects like swords, relics, and mana rocks. Equipment is a subtype of artifact that attaches to creatures to boost them. If you encountered "item" in a Universes Beyond set (like the Fallout or Final Fantasy crossovers), it's likely flavor text or a creature/token name rather than a rules term.
If you saw "Item" on a specific card or in a particular product, let me know the exact wording or card name, and I'll explain precisely how it functions and where it matters in Commander.