What does renal calculi refer to?

Explanation

### Step-by-Step Solution:

1. **Definition of Renal Calculi**: Renal calculi are commonly known as kidney stones. They refer to hard deposits that form in the kidneys.

2. **Composition**: These stones are primarily composed of minerals and salts. A significant component is calcium oxalate, but they can also include other minerals and salts.

3. **Formation**: Kidney stones form due to an excess of certain substances in the diet and body weight. When there is an imbalance, these substances can crystallize and form stones.

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