A P2TR output is a 32-byte x-only key Q = P + t·G, where t is a tagged hash of the internal key P and the Merkle root of alternative scripts. Spending by key path is a single 64-byte BIP-340 signature, indistinguishable whether the key belongs to one person or a MuSig2 group; spending by script path reveals only the executed script and a Merkle proof. Tapscript (BIP-342) replaces OP_CHECKMULTISIG with OP_CHECKSIGADD.
Benefits are smaller and more private multisig, cheaper complex scripts and a new signature hash (BIP-341) that commits to all input amounts, which simplifies hardware-wallet fee verification. Message signing for P2TR addresses requires BIP-322.