Not all construction contracts have final certificates, but those that do generally require a certain procedure to be followed prior to issue of the certificate. It is important that all parties follow this procedure and understand the implications of it.
The final certificate is issued after the completion of the works, and contains a final calculation of the sums due under the contract.
It normally marks the conclusion of the project and is intended to signify that all matters that need to be resolved have been resolved. There are potentially extremely serious consequences if prompt action is not taken where parties disagree with the final certificate.