"Elbow grease" is a colloquial term that refers to hard work, effort, or physical labor, especially when it involves cleaning or polishing something. The phrase "elbow grease gives the best polish" emphasizes that putting in effort and working diligently can yield excellent results.

In practical terms, this means that using muscle power and spending time on a task often results in a better outcome than simply relying on products or shortcuts alone. For example, manually scrubbing a surface might take more effort than using a chemical cleaner, but it can lead to a superior clean and shine.

So, while the phrase is figurative, it encourages people to put in genuine effort for the best results.