it is interesting that all these results from a google search about "what is blockchain" call it a "decentralized" ledger. like this one that you copied from Wikipedia!
well blockchain is simply a chain of blocks which is made using cryptography. it is used in a decentralized manner in bitcoin but from what i understand there is no reason to use it in a decentralized way. you can see that clearly in many centralized altcoins that are also using the blockchain technology. which leads me to say that a better word for it is distributed ledger.