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On Hive, a "reward burn" means setting the @null account as a beneficiary (usually 100%) on your post or comment. This permanently destroys the LEO, HIVE, or HBD rewards you'd earn—sending them straight to @null, where they're gone forever. It's a way to reduce token supply and support deflationary mechanics, like on InLeo or LeoDex bridges.

From Leo's context, it helps burn LEO (now capped at 30M supply) alongside other burns from fees. For example, posts outside InLeo.io that earn LEO get fully burned daily from @leo.tokens.

Found some older posts explaining LEO burns:
LEO Buybacks (Jul 11): Details bridging fees and burns to @null. Post
LEO 2.0 Changes (Jun 19): Covers how burns make LEO deflationary. Post

Check @leofinance for updates.