Berry Glitch is the catch-all nickname for a spread of glitches that occur in Pokémon Ruby/Sapphire approximately one real-time year after a new save has started. Basically, the game's day counter stops moving. This brings a halt to all time-based events such as berries growing, the Lilycove Dept Store's sale, and trainer re-battles. Luckily, Nintendo has used all subsequent Pokémon games as trojan horses to install a patch for this glitch, so serious players will probably never have to worry about it.