Protocol & upgrades
Bitcoin has no release manager. It has a proposal process, several implementations, and a large number of people who can simply refuse to run your code. This section explains how a change actually lands.
A BIP is a Bitcoin Improvement Proposal, a numbered document in a public repository. Being numbered says nothing about acceptance, and most BIPs go nowhere. The ones that matter got activated, and the words for how that happens are here: soft fork for a rules tightening change old nodes still accept, hard fork for one they do not, and the activation mechanisms that have been argued over more fiercely than the changes themselves.
SegWit and Taproot are the two upgrades most likely to turn up on an exchange withdrawal screen. SegWit moved signature data out of the part of the block that counts against the size limit, which cut fees for wallets that adopted it. Taproot added Schnorr signatures and made complex spending conditions look ordinary on chain, which is a privacy improvement as much as a capability one.
The section also carries the arguments that are still open rather than settled: covenants and the proposals that would enable them, OP_CHECKTEMPLATEVERIFY and OP_CAT, and the Ordinals, inscriptions and Runes fight over what block space is for. The measurements those arguments run on, block weight and the maximum block size, are defined under mining and consensus.
28 terms. Last reviewed 2026-08-13.
Terms in Protocol & upgrades
- Bitcoin Improvement Proposalalso BIPA Bitcoin Improvement Proposal is a numbered design document that describes a change to bitcoin or a standard for wallets to follow, with no authority to impose it.
- BRC-20BRC-20 is an experimental token standard that writes JSON text into ordinal inscriptions and leaves every balance to be computed by off-chain indexers rather than by bitcoin.
- Cluster mempoolCluster mempool is the redesign of Bitcoin Core's waiting room that keeps every group of connected unconfirmed transactions sorted, so the node always knows which ones a miner would actually pick.
- Compact block relayalso BIP152Compact block relay replaces a new block on the wire with a list of six-byte identifiers, which the receiving node matches against transactions it already holds and reassembles locally.
- CovenantA covenant is a spending rule that limits where bitcoin can go next, not just who may move it, and no opcode in Bitcoin Script can enforce one today.
- Ephemeral anchorAn ephemeral anchor is a zero-value output added to a transaction purely so that somebody can attach a fee-paying child and drag the parent into a block.
- ErlayErlay is a proposed way for nodes to compare notes on which transactions they have seen using tiny sketches, instead of shouting every transaction hash at every peer.
- ForkA fork is any point where bitcoin's history or its rulebook splits in two, which is why the word covers three different events that resolve on completely different timescales.
- Hard forkA hard fork loosens or changes bitcoin's rules so that blocks the old software rejects become valid, which means every node must upgrade or be left behind on a different chain.
- Inscriptionalso Ordinal inscriptionAn inscription is a file stored inside a Taproot witness and attached to one satoshi, which is how images, text, and collectibles ended up living on bitcoin itself.
- MASTalso Merkelized Alternative Script TreeMAST hides every spending condition you do not use behind a Merkle tree, so revealing one branch when you spend keeps the rest private and off the blockchain.
- Miner-activated soft forkalso MASFA miner-activated soft fork switches on when a supermajority of mined blocks signals for it, using the block version field as a vote counted automatically by every node.
- MiniscriptMiniscript is a structured way of writing the useful subset of Bitcoin Script so that software can analyze a spending policy, work out its costs, and sign for it automatically.
- MuSig2also Key aggregationMuSig2 lets several signers combine their public keys into one and produce a single 64-byte Schnorr signature, so a group spend looks identical to a solo spend on chain.
- OP_CATOP_CAT joins the top two items on the script stack into one, an operation Satoshi disabled in 2010 and that BIP-347 proposes to restore inside tapscript.
- OP_CHECKLOCKTIMEVERIFYalso CLTV, BIP65OP_CHECKLOCKTIMEVERIFY is the script opcode that stops a coin being spent before a stated block height or calendar date, no matter who holds the key.
- OP_CHECKSEQUENCEVERIFYalso CSV, BIP112OP_CHECKSEQUENCEVERIFY locks a coin for a stretch of time measured from its own confirmation, failing any spend whose input has not waited long enough.
- OP_CHECKSIGADDOP_CHECKSIGADD counts signatures one key at a time inside tapscript, replacing the old multisig opcode with a check that batch verification and future key types can both handle.
- OP_CHECKTEMPLATEVERIFYalso CTV, BIP119OP_CHECKTEMPLATEVERIFY is a proposed opcode that would let an output commit in advance to the exact transaction allowed to spend it, down to its outputs and amounts.
- Ordinalsalso Ordinal theoryOrdinals is a numbering scheme that assigns every satoshi a serial number in mining order and tracks it through transactions, giving individual units of bitcoin an identity.
- Runesalso Runes protocolRunes is a token protocol that records issuance and transfers in a single OP_RETURN output, so balances ride on unspent outputs instead of on inscribed text files.
- Schnorr signaturealso BIP340A Schnorr signature is the 64-byte signature scheme bitcoin adopted with Taproot, and its defining property is linearity: several keys and signatures add together into one.
- SegWitalso Segregated Witness, BIP141SegWit moved signature data out of the part of a transaction that the txid commits to, fixing transaction malleability and raising block capacity without changing the one megabyte base limit.
- Soft forkA soft fork tightens bitcoin's rules so that blocks valid under the new software are still valid under the old, letting the network upgrade without anybody being forced off the chain.
- Taprootalso BIP341Taproot is the 2021 soft fork that gave bitcoin Schnorr signatures and a new output type where the cooperative spending path looks identical to an ordinary single-key payment.
- TapscriptTapscript is the version of Bitcoin Script that runs inside Taproot script path spends, with Schnorr signatures, no opcode ceiling, and a signature budget in place of the old counters.
- User-activated soft forkalso UASFA user-activated soft fork enforces a new rule on a flag day chosen by node operators, so miners who ignore it find their blocks rejected rather than merely outvoted.
- Witness dataalso WitnessWitness data is the signature material a SegWit transaction carries in a separate section, discounted to one weight unit per byte and excluded from the txid entirely.
The other 13 sections
- BasicsWhat bitcoin is, what a satoshi is, and the handful of ideas the rest of the glossary is built on.
- Addresses & keysWhere coins get sent, what a private key actually controls, and how one seed produces thousands of addresses.
- Wallets & custodyHot, cold, custodial and multisig, and what each one changes about who can move your coins.
- Privacy & securityThe attacks that take people's bitcoin, and the habits and tools that stop them.
- Transactions & feesWhat a bitcoin transaction is made of, why it costs what it costs, and how to unstick one.
- Buying & exchangesOrder types, spreads and fee schedules: the vocabulary an exchange uses while it is charging you.
- Markets & investingMarket cap, volatility and spot ETFs. The language of price, without the price predictions.
- Mining & consensusHow new blocks get made, what difficulty adjusts, and why the rules hold with nobody in charge.
- Lightning & layer 2Payment channels, invoices and routing, for moving bitcoin without paying for space in a block.
- Regulation & taxKYC, the Travel Rule, MiCA and capital gains: the rules that reach your account and your tax return.
- Culture & historyMt. Gox, the genesis block, HODL, and the events and slang that shaped how people talk about bitcoin.
- Nodes & softwareBitcoin Core, full nodes, pruning and RPC: the software that enforces the rules.
- Developer referenceP2P message types, opcodes and script terms: the field names you meet reading bitcoin code.