Bitcoin is a stack of computers (or nodes) that all run Bitcoin's code and store the blockchain. A blockchain can be thought of as a stack of blocks. Each block contains a stack of transactions. No one can deceive the system as all these computers running the blockchain have the same block and transaction list and can transparently see that these new blocks are populated with new Bitcoin transactions. (Regardless of whether the Bitcoin "node" is running or not), anyone can see that these transactions are happening live. A malicious actor needs to run 51% of the computing power that makes up Bitcoin to behave badly. Considering that Bitcoin has approximately 47,000 nodes as of May 20 and this number is increasing gradually, it is unlikely that such an attack will succeed.

People involved in the Bitcoin network with Bitcoin nodes (nodes or computers) will likely be forked into a new blockchain if an attack occurs, which negates the effort of the evil actor to carry out the attack.

Bitcoin is a type of cryptocurrency. The balances of Bitcoin tokens (coins) are kept using public and private "keys", which are long strings of numbers and letters that are linked together through the mathematical encryption algorithm used to generate them. The public key (just like a bank account number) acts as the address published to the world where others can send bitcoins. The private key (just like an ATM PIN) must be protected as a secret and is used only to authorize Bitcoin transfers. Bitcoin keys should not be confused with the Bitcoin wallet, a physical or digital device that facilitates Bitcoin trading and allows users to track coin ownership (the amount they have). The term "wallet" is somewhat misleading because of Bitcoin's decentralized nature. Decentralized nature means that the amount is never "stored" in a wallet, rather it is stored decentrally in a blockchain.

Style notes: According to the official Bitcoin Foundation, the word "Bitcoin" is capitalized in order to refer to the entity or concept, while "bitcoin" refers to an amount of the currency or the units themselves (eg "I bought 20 bitcoins.") Plural the format can be "bitcoin" or "bitcoins". Bitcoin is also often written as "BTC" in short.