The Free TON blockchain consists of multiple sub-blockchains. The two types of these blockchains are:
• A unique master blockchain, or masterchain for short, contains general information about the protocol and the current values of its parameters, the set of validators and their stakes, the set of currently active workchains and their shards, and most importantly, the set of hashes of the most recent blocks of all workchains and shardchains.
• Several working blockchains, or workchains for short, contain the value-transfer and smart contract transactions. Different workchains may have different rules, meaning different formats of account addresses, different formats of transactions, different virtual machines for smart contracts, different basic cryptocurrencies and so on. Nonetheless, they must all satisfy certain basic interoperability criteria to make interaction between different workchains possible and relatively simple. Workchanis have lower fees and are preferable for regular wallets and, generally, for any smart contracts not critical to Free TON operation.
Accounts are assigned to certain blockchains, according to the first number of the address: -1 for the masterchain and 0 for a workchain.
To learn more, refer to ton.dev documentation of the subject.