Define heat with its S.I Unit

Explanation

**Step-by-Step Solution:**

1. **Definition of Heat:**
Heat is defined as a form of energy that is transferred between two systems or bodies due to a temperature difference. This transfer occurs spontaneously from a region of higher temperature to a region of lower temperature.

2. **Conditions for Heat Flow:**
- Heat flows only when there is a temperature difference between two bodies or systems.
- The direction of heat flow is always from the higher temperature to the lower temperature.
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