The CDM Glossary defines operational lifetime as:
...the period during which the project activity is in operation (CDM Glossary of Terms, Version 03).
The operational lifetime of the project can be distinguished from the crediting period for the project. While the operational lifetime is the time over which the project is actually operating, the crediting period is the period during which the project is generating certified emission reductions (CERs).
The operational lifetime begins with the project's starting date and ends with its decommissioning, while the crediting period usually runs from the date of registration to the end of the fixed or renewable period selected by project participants.
A project may continue operating after the end of the crediting period, and subject to additionality considerations, may begin operating before the commencement of the crediting period. However, the crediting period must not end after the end of the project's operational lifetime:
No crediting period shall end after the end of the operational lifetime (calculated as from starting date) (CDM Glossary of Terms, Version 03).