Blockchain is where transactions or data records are grouped into blocks, with each block linked to the next by a hash, and identical copies are maintained by many network participants — it's a distributed ledger.
If one person keeps the only copy of a book, it's hard to tell if they've edited it. But if a hundred people hold identical copies, and every new page needs everyone to check and agree before it's added, editing or deleting becomes very hard. That's the basic idea behind blockchain.
Block
A data package containing transaction records.
Chain
The sequence formed by linking each block to the previous hash.
Ledger
A digital record book shared among everyone.
Network
The nodes that check, store, and update the ledger.
You should see
Blockchain = shared ledger + cryptographic linking + network agreement.