This is my excuse for why I have no idea what "performance optimization" entails or means. Now to convince interviewers..
In a context of an interview it means how performance of an algorithm scales with respect to the input length. This is measured in Big O notation. Understanding that is seldom very helpful on the job, but it's very important for interviews, so make sure you learn it.
That's not specific enough. Memory usage, elapsed time, and energy usage are all functions of the input size, and each is a different optimization problem. Instead of talking about performance optimization, you should be talking about memory optimization or speed optimization.
Do you mean speed? Efficiency? Accuracy? Say what you mean.