Benchmarking is the process of comparing two or more systems or processes under controlled circumstances in order to have a quantitative measure with which to compare or rank them. The benchmarking tag should be used for questions about how to perform benchmarking tasks or theory questions, not for lists of benchmarking results or requests for benchmarking data; those questions are off-topic for Stack Overflow.
Benchmarking is the process of comparing two or more systems or processes under controlled circumstances in order to have a quantitative measure with which to compare or rank them.
For hardware, benchmarking typically involves either performing a simple task many times or a complex task to ascertain the performance characteristics desired (often speed, but power draw, heat, memory usage, and other characteristics may be of interest as well). Common benchmark operations include FLOPS (Floating Point Operations Per Second), write or read time for a large file, write or read time for many small files, rendering large images, and downloading or uploading large files over a network.
For software, benchmarking typically involves running the different software of interest (different versions of a program, different programs that accomplish a similar task, etc.) on an identical system (either one system, or two identical systems) and performing tasks that take sufficient time to notice a difference. This is often performed on very small differences in code, such as to verify which approach is superior to solving a particular problem.
Benchmarking also includes industry standard benchmarks and common benchmarking suites, used to assist users in making purchasing decisions or otherwise comparing their current systems to other available systems. However, it should be used in this context for issues with building or understanding the code and behavior of these benchmarks, not for general recommendations on the benchmarks suites or on the tested products.
Include additional tags to your question to indicate what type of benchmarking the question is about, such as hardware, or what type of programming language if software, etc.