A benchmark fixes the tasks, the data and the scoring rules, so that different tools or models can be compared fairly. In AI, security benchmarks measure things such as how well a model finds vulnerabilities, writes exploits or answers security questions.
The word has another common meaning. The CIS Benchmarks are configuration guides that describe secure settings for operating systems and products, and are used to check whether a system is hardened. Which meaning applies depends on context.
Benchmark results should be read with care. A model can score well on a benchmark and still perform poorly on your own code, particularly if the benchmark data leaked into its training material or if the tasks are unlike real work.
Check what a benchmark measures, how it is scored and whether the test data was kept separate, and run your own tests on your own systems before you rely on a score.