Taproot is not a smart contract in the traditional sense, but it is an upgrade to Bitcoin's scripting language that can enable more advanced smart contract functionality. Taproot is a soft fork upgrade that was activated on the Bitcoin network in November 2021.

One of the main benefits of the Taproot upgrade is that it improves Bitcoin's privacy and security by allowing more complex transactions to be executed while appearing as a simple transaction on the blockchain. This is achieved through a technique called "Merkleized Abstract Syntax Trees" (MAST), which allows multiple possible spending conditions to be hidden within a single transaction, making it difficult for external parties to determine which conditions were actually used.

Taproot also enables the implementation of advanced multi-signature schemes, which can be used to enhance the security of Bitcoin transactions. With Taproot, multiple signatures can be aggregated into a single signature, reducing the amount of data needed to be stored on the blockchain. This reduces transaction fees and allows for more efficient use of Bitcoin's limited block space.

In terms of its relationship to SegWit, Segregated Witness (SegWit) was a previous soft fork upgrade that was activated on the Bitcoin network in August 2017. SegWit separated the transaction signature data from the transaction data, which allowed for more transactions to be included in each block. Taproot builds upon SegWit by further optimizing the way transactions are structured and by enabling more advanced smart contract functionality.

In summary, Taproot is an upgrade to Bitcoin's scripting language that enhances privacy, security, and scalability while enabling more advanced smart contract functionality. It builds upon the benefits of SegWit by further optimizing transaction structure and enabling more complex spending conditions to be hidden within a single transaction.