In semiconductor physics, what is meant by:
A rectifier,

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept of Rectification**:
- Rectification is the process of converting alternating current (AC) into direct current (DC). This is essential in many electronic applications where a stable DC voltage is required.

2. **Definition of a Rectifier**:
- A rectifier is defined as an electronic device that performs the function of rectification. It uses semiconductor materials, specifically p-n junction diodes, to achieve this conversion.

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