It is a mapping between Ethereum addresses and account states. The addresses are 20 bytes (160 bits) long. This mapping is a data structure that is serialized using Recursive Length Prefix (RLP).
RLP is a specially developed encoding scheme that is used in Ethereum to serialize binary data for storage or transmission over the network and also to save the state in a Patricia tree on storage media. The RLP function takes an item as an input, which can be a string or a list of items and produces raw bytes that are suitable for storage and transmission over the network. RLP does not encode data; instead, its primary purpose is to encode structures.
