What is residual body?

Explanation

### Step-by-Step Solution:

1. **Definition of Residual Body**: A residual body is a type of secondary lysosome that contains undigested substances.

2. **Formation of Residual Bodies**: Residual bodies are formed when lysosomes digest cellular materials, but some substances remain undigested.

3. **Composition**: The residual body consists of these undigested materials that could not be broken down by the lysosomal enzymes.

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