In Pokemon GO, a special trade is a trade between two players that involves rare or special Pokemon. These trades require more Stardust to complete than regular trades and can only be completed once per day. The following types of Pokemon are considered special trades:

• Pokemon not already in your Pokedex
• Legendary Pokemon
• Shiny Pokemon
• Pokemon with forms not already in your collection (such as Unown letters or holiday-exclusive Pikachus)
• Purified versions of shadow Pokemon

Players can reduce the amount of Stardust required for a special trade by increasing their Friendship level with the other player. The cost of a special trade can also vary depending on whether the Pokemon being traded is already in the recipients Pokedex. Its important to note that the cost of a special trade can be quite high, especially for rare or legendary Pokemon.