An abbreviation for “number only used once”, Nonce refers to a number that is added to either a hashed or encrypted block in a blockchain that, upon rehashing, would meet the difficulty level restrictions.

Nonce is the number that blockchain miners solve for. Simply put, it is an arbitrary number that should only be used once upon its creation. The process is done by processing the block input through a function which in turn produces an output of a fixed length. When the mathematical computations are duly solved by the miner, he or she would be gifted with cryptocurrency for the time and skill offered. 

Nonce is actually challenging to find and is considered a way to filter out the less skilled crypto miners.