Optimization is the process of improving an existing program to make it work more efficiently or/and using less resources.
Since optimization may occur at various stages (analysis, design, implementation, compiler, runtime, etc.) during the development of a program, and according to the FAQ, the following types of questions are certainly valid:
- What is/is it considered optimization, with a detailed question about what you are referring to (remember that "programmers" is not "code review"). Theoretical questions on algorithms efficiency are OK.
- What can(not) be optimized given a context (for example #1 or #2).
Beware that some more "general" questions about optimization have already been asked. Most notably "when to perform optimization", "when to stop optimizing", "is premature optimization really bad"...
More information on optimization may be found on Wikipedia: Optimization.