It is an arbitrary number that is used only once in the cryptographic communication. It is often a pseudo-random or random number hand out in a verification protocol to confirm that old statement cannot be used again in replay attacks. They can also be beneficial in cryptographic hash functions and as initialization vectors.
A nonce is a random number the block-chain miners are solving for. The process of adding transactions to block-chain involves multiple computer processing command. The companies and individuals who process cryptocurrency blocks are called miners.
The nonce is much challenging to discover and is deliberated a system to weed out the inexperienced block-chain miners. The block-chain miners need to find the number formerly solving for a block in block-chain. Once the miners solve the mathematical calculations, they are awarded cryptocurrency for their skill and time.