From CryptoWiki

  • This is the measure of how hard it is to generate a new block in the blockchain.  The difficulty is designed to adjust every 2,016 blocks (roughly 2 weeks) to balance out the rate at which blocks are created.  The difficulty has an absolute minimum of 1, but not such limit exists for the maximum.
  • A network-wide setting that controls how much computation is required to produce a proof of work.