Mining Difficulty

Mining Difficulty is a metric that reflects the adjustment automatically made by the Horizen network to insure that new blocks are generated at an average of every 2.5 minutes.

This is important, because as the available hash power (block-finding capacity) on the network goes up (or down), blocks will be generated too fast (or too slowly). Think in terms of inflation or deflation of a fiat currency, such as $US or the EURO. Adjusting the mining difficulty prevents either of these undesirable conditions.

The actual formula for the mining difficulty adjustment can be found in the Zen White Paper.

Source: Horizen White Papers - Original Whitepaper, Section 3 Specifications at Launch

You can view the adjustments made to mining difficulty at:

https://www.coinwarz.com/difficulty-charts/horizen-difficulty-chart