Blockchain gets explained in either oversimplified buzzwords or impenetrable technical detail. The core concept is more intuitive than either extreme suggests.
Picture a shared notebook that thousands of computers around the world each keep an identical copy of. Every time a new transaction happens, it gets bundled with other recent transactions into a “block,” and that block gets added to everyone’s notebook simultaneously, with a special code linking it to the previous block — that linking is the “chain” in blockchain.
Because everyone holds an identical copy and new blocks reference previous ones, altering a past transaction would require simultaneously changing it across the vast majority of all those distributed copies at once — which is what makes the record practically tamper-resistant rather than relying on a single central authority to keep it honest.
This distributed, tamper-resistant record-keeping is the actual innovation — cryptocurrency is simply the first widely adopted application built on top of it.