Steem Simplicity 0.17.0: The hardfork is schedule for Tue, 21 March 2017 15:00:00 UTC (11:00:00 EDT)

What exactly is a hard fork?

I think the easiest way to think about a hard fork is thinking of a mathematical set with elements in it. The elements inside of this set represent consensus rules for the blockchain network. Whenever an element is removed from this mathematical set, it is a hard fork.