Basically the word cryptocurrency means "cryptographic currency", which, by definition is, this is a form of currency that only exists digitally, can't be regulated by the central authority and it uses a decentralized system to record the transaction and management of new units to prevent counterfeiting and fraudulent transactions.
In the cryptocurrency sector, the Blockchain is used to order transactions. Blockchains are the only way (probably) to maintain the transactions. Because cryptocurrencies has no centralized issues or records, currency's like PayPal or Payoneer is not a cryptocurrency.
well, the blockchain systems are a natural fit for monetary systems, so you can change your cryptocurrency to dollar or other currencies by Coinbase website.
cryptocurrencies are called softwares, and that depends on networking hardware. so in the cryptography, computing and networking are equally important to the function of cryptocurrencies.
