Which of the following is NOT a phase in the Software Development Lifecycle (SDLC)?

The Software Development Lifecycle (SDLC) consists of several key phases that guide the development process from conception to deployment and maintenance. Among the phases commonly recognized are Requirement Analysis, Deployment, and Testing. These stages play distinct roles: Requirement Analysis focuses on gathering and defining what the software needs to accomplish. Testing involves evaluating the software to ensure it meets the specified requirements and is free from defects. Deployment is the process of making the software available for users after development and testing.

Optimization, while important in the context of improving existing software, is not typically classified as a formal phase within the SDLC. Instead, it is often considered a part of maintenance or an ongoing process that occurs after deployment to enhance performance or address other aspects of the software. As such, it does not fit neatly into the established phases of the SDLC, making it the correct choice for this question.