What does "difficulty" mean on a stratum mining pool? : BitcoinMining

What does "difficulty" mean on a stratum mining pool? : BitcoinMining:

"Worker's speed Difficulty

<500                 Mhash/s 1

  500-1000        Mhash/s 2

  1000-2000      Mhash/s 4

  2000-4000      Mhash/s 8

  4000-10000    Mhash/s 16

  10000-40000  Mhash/s 32

 >40000            Mhash/s 64"



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