What is Bitcoin?

• Bitcoin is a payment system invented by Satoshi Nakamoto, who published the invention in 2008. 
• The system is peer-to-peer; users can transact directly without needing an intermediary. 
• The ledger uses its own unit of account, also called bitcoin.
• Transactions are verified by network nodes and recorded in a public distributed ledger called the block chain.
•  The system works without a central repository or single administrator, which has led theUS Treasury to categorize it as a decentralized virtual currency.
•  Bitcoin is often called the first cryptocurrency.
• Bitcoin is more correctly described as the first decentralized digital currency.

Bitcoins are created as a reward for payment processing work in which users offer their computing power to verify and record payments into the public ledger. This activity is called mining and is rewarded by transaction fees and newly created bitcoins.Besides mining, bitcoins can be obtained in exchange for different currencies,products, and services. Users can send and receive bitcoins for an optional transaction fee.

Subunit
10−3	millibitcoin
10−6	microbitcoin, bit
10−8	satoshi[4]
Symbol	BTC, XBT,
millibitcoin	mBTC
microbitcoin, bit	μBTC

The unit of account of the bitcoin system is bitcoin. Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), microbitcoin (µBTC), and satoshi. Named in homage to bitcoin's creator, a satoshi is the smallest amount within bitcoin representing 0.00000001 bitcoin, one hundred millionth of a bitcoin. A millibitcoin equals to 0.001 bitcoin, which is one thousandth of bitcoin. One microbitcoin equals to 0.000001 bitcoin, which is one millionth of bitcoin. A microbitcoin is sometimes referred to as a bit.

Wallets

A wallet stores the information necessary to transact bitcoins. While wallets are often described as a place to hold or store bitcoins,due to the nature of the system, bitcoins are inseparable from the block chain transaction ledger. Perhaps a better way to describe a wallet is something that "stores the digital credentials for your bitcoin holdings" and allows you to access (and spend) them. Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated. At its most basic, a wallet is a collection of these keys.

There are several types of wallet. Software wallets connect to the network and allow spending bitcoins in addition to holding the credentials that prove ownership. Internet services called online wallets like Blockchain.info, Circle, or Coinbase offer similar functionality but may be easier to use; in essence, bitcoin credentials are stored with the online wallet provider rather than on the user's hardware. Physical wallets also exist and are more secure, as they store the credentials necessary to spend bitcoins offline. Examples combine a novelty coin with these credentials printed on metal, wood, or plastic. Others are simply paper printouts. Another type of wallet called a hardware wallet keeps credentials offline while facilitating transactions.