Methematical constants, `pi, etc.` are called ……….. .

Answer

To solve the question regarding the mathematical constant pi, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the term that describes mathematical constants like pi. We need to identify the specific category or classification of such constants.

2. **Identifying Pi**: Pi (π) is a well-known mathematical constant that represents the ratio of the circumference of a circle to its diameter. Its approximate value is 3.14, and it can also be expressed as the fraction 22/7.

3. **Characteristics of Pi**:
- Pi is a constant, meaning it has a fixed value that does not change.
- It is a dimensionless quantity, which means it does not have any physical units associated with it.

4. **Conclusion**: Based on the characteristics of pi, we can conclude that it falls under the category of "dimensionless constants."

5. **Final Answer**: Therefore, the fill-in-the-blank answer is: "Mathematical constant pi is called a dimensionless constant."