What is a couple? What is its action?

Explanation

### Step-by-Step Solution:

1. **Definition of a Couple**:
A couple is defined as a system of two equal and opposite forces that act on a body at two different points. These forces are parallel and have the same line of action.

2. **Characteristics of a Couple**:
- The two forces are equal in magnitude.
- The two forces are opposite in direction.
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