Update blockchain.md

knowledge-base/moneropedia/blockchain.md

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 layout: moneropedia
 entry: "Blockchain"
 terms: ["blockchain", "blockchains"]
-summary: "a distributed ledger of all transactions both past and present, without revealing who the funds came from or went to"
+summary: "A blockchain is a distrubuted database that continuously grows with a record of all of the transactions that have occurred with a given cryptocurrency.  This database is often referred to as a ledger because the data contains a large list of transctions that have taken place.  In Monero, these transactions are packaged together into 'blocks' every 2 minutes (on average) and all miners and nodes on the network have copies of these blocks.  One of the unique features of Monero, as compared to other cryptocurrencies such as Bitcoin, is that transactions in the Monero blockchain do not reveal who the funds came from or went to.  Each individual monero user controls who can see their transactions with a key called the 'view key'."
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 ### The Basics