A “rule of thumb” is a general principle or guideline that’s intended to offer practical, often quick advice rather than precise instructions. It’s a way of saying, “Here’s a good rule to follow most of the time.”
This heuristic doesn’t necessarily have an exact science behind it; it’s more about what has worked well in practice. In other words, it’s a useful rule for most situations but not a strict rule or law.
The rule of thumb gives a general sense of direction, especially when exact measurements or detailed procedures aren’t necessary. For example, in cooking, a good rule of thumb is to add salt to taste. There’s no strict amount that applies to every dish, but the guideline helps you use your best judgment.