In non-technical language, Bitcoin is a digital currency in which transactions can be performed without the need for a credit card or central bank. It's designed to enable users to send money over the Internet in a very simple and efficient way.
In short, no one runs Bitcoin. Bitcoin is run collectively by the users who uses the Bitcoin Client, and any changes to the Bitcoin system have to be approved by the majority of users before they are implemented.
A Bitcoin address is a unique identifier which allows you to receive Bitcoins. With PayPal you send funds to an email address, and similarly with Bitcoin you send funds to a Bitcoin address. For example, this is one of our Bitcoin addresses: 1LjiSp75s24oBk5PkXVzNqCFr6ePcgv551
Please verify that you have copied the destination address exactly before sending Bitcoins to it. Bitcoin transactions are not reversible!
A private key is a secret code which allows the user to prove his ownership of his Bitcoins. Every Bitcoin address has a matching private key, which is saved in the wallet file of the person who owns the balance. The private key is mathematically related to the Bitcoin address, and is designed so that the Bitcoin address can be calculated from the private key, but importantly, the same cannot be done in reverse.
Please keep your private keys safe, and make periodic backups to prevent the loss of Bitcoins. Anyone with your private keys can spend your Bitcoins!
At the moment, many transactions are typically processed in a way where no fee is expected at all, but for transactions which draw coins from many Bitcoin addresses and therefore have a large data size, a small transaction fee is usually expected.
Please see the bitcoin wiki for calculating minimum fees.
It means that the transaction has not yet been included in the blockchain, and is still reversible. A transaction typically takes around 10 minutes to be confirmed. When that happens, it is said that one confirmation has occurred for the transaction. With each subsequent block that is found, the number of confirmations is increased by one. To protect against double spending, a transaction should not be considered as confirmed until a certain number of confirmations is seen.
The blockchain is a public ledger of all transactions in the Bitcoin network. Blockchain.info allows you to navigate the bitcoin blockchain. We also operate Bitcoin's largest and most secure wallet service.
Miners are individuals who run computer systems to repeatedly calculate
hashes with the intention to create a successful block and earn coins from
transaction fees and new coins created with the block itself. The term
references an analogy of gold miners who dig gold out of the ground and
thus 'discover' new gold that can be used to create new coins, with a similar
kind of discovery occurring with a successful hash to create new Bitcoins.
The number of Bitcoins in existence will never exceed 21 million. To see how many Bitcoins are in circulation, please go to: https://blockchain.info/charts/total-bitcoins
The current market price for a Bitcoin is always changing due to the supply and demand for it. Bitcoins are traded at Bitcoin Exchanges. A historical Bitcoin price chart can be found at: https://blockchain.info/charts/market-price
Bitcoin clients are the base level of technology for conducting Bitcoin transactions, and they store the keys needed to conduct a Bitcoin transaction. They come in multiple flavors, and are customized to fit different niches.
The Bitcoin-QT Client (Downloadable at http://bitcoin.org/) is the original software written by Satoshi Nakamoto, the project's founder. If you aren't sure which program to pick, this is a good bet. It is suited for enthusiasts, merchants, miners, developers and people who want to help support the project.
The MultiBit Client (Downloadable at https://multibit.org/) is fast and easy to use, even for people with no technical knowledge. It is also able to import Blockchain.info's wallet backups (Multibit version 5.17 and earlier), making it a versatile tool for all kinds of users.
The Electrum Client (Downloadable at http://electrum.org/) focuses at speed, with low resource usage and simplifying Bitcoin usage. Startup times are instant because it operates in conjunction with high-performance servers that handle the most complicated parts of the Bitcoin system.
Blockchain.info is also a form of Bitcoin client. We provide a web-based client with emphasis on speed, security, and ease of use.