A Bitcoin Unspent Transaction Output. It is defined by a transaction hash and a vout index which, collectively, constitute an outpoint.

Simple Payment Verification (SPV) allows a transaction receiver to confirm that the sender has control of the source funds of the payment they are offering, without needing to download the entire blockchain. This is achieved using Merkle proofs.

The OP_RETURN standard locking script just contains the OP_RETURN opcode followed by one or more data pushes. The standard OP_RETURN script has a maximum size limit of 83 bytes. However, there is an ongoing discussion and corresponding pull request to relax these standardness restrictions.

Cells are the primary state units in CKB, within them users can include arbitrary states. All data on Nervos CKB is stored in Cells. A Cell has 4 fields: capacity, data, type and lock.

A Script in CKB is a binary executable that can be executed on-chain. It is a program that runs on a virtual machine powered by the RISC-V instruction set, called the CKB-VM, and can perform arbitrary logic to guard and protect your Cells. You can think of it as smart contract.

Extensible UDT(xUDT) is the User-Defined-Token(fungible token) Script implementation on CKB. You can think of it as the ERC-20 smart contract on Ethereum.

A one-to-one mapping mechanism in RGB++ that links Bitcoin UTXOs to CKB Cells, enabling ownership synchronization through Bitcoin's UTXO locks while maintaining state in CKB's Cell data and type fields. This binding allows for Turing-complete Bitcoin UTXO transactions validated by CKB Cells.

A Merkle Mountain Range (MMR) is a binary hash tree data structure designed to allow efficient appending of new leaves while maintaining the integrity of the existing nodes. A MMR proof can be utilized to verify whether a specific item is included in the MMR root.

A merkle root is created by hashing together pairs of TXIDs to get a short and unique fingerprint for all the transactions in a block. This merkle root is placed in a block header to prevent the contents of the block from being tampered with later on.