Complete performance of a contractual obligation by a third party on behalf of a party to the contract, e.g. performance by a subcontractor or employee. Vicarious performance will be valid unless personal performance is demanded by the terms or nature of the contract.
For example, if X engages and contracts with Y to build a fence, and Y subcontracts Z to build it, which Z does as per the terms of the contract, valid vicarious performance has taken place. However, if for example A engages and contracts with B to paint a mural, and B instructs C to paint it, the vicarious performance of C may be invalid if the contract considered B’s artistry and/or style as part of the product.