The Blockchain lets you use the Internet to securely transact with anyone without any middleman. Like the Internet, no one is in charge and it is nearly impossible to shut down. It will disrupt all the intermediaries we currently use to exchange value and serve as trusted parties, including banks, financial markets, and governments.
Blockchain technology refers to various schemes that use cryptography and consensus algorithms to allow multiple parties to share a database where no central party is in control. This allows multiple untrusted parties to transact and keep records in transparent and fully auditable manner.
Sometimes blockchain technology is used to describe non-financial uses of the Bitcoin blockchain such as securing medical records or issuing a digital asset that represents a vehicle.
Overall, blockchain technology is over-hyped, underestimated, and generally misunderstood. The phrase has become so misused that it's meaning is nebulous.