Winnow is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Destroy target nonland permanent if another permanent with the same name is on the battlefield. Draw a card.

How it works : Winnow

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Winnow.

Invasion of Lorwyn // Winnowing Forces

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.) When this Siege enters, destroy target non-Elf creature an opponent controls with power X or less, where X is the number of lands you control. Winnowing Forces's power and toughness are each equal to the number of lands you control.