What is the numerical prefix for the term that refers to 'three'?

The term "tri" is a numerical prefix that signifies the quantity 'three.' This prefix is commonly used in various scientific and mathematical contexts. For instance, a triangle has three sides, and triceps muscles are comprised of three heads. The use of "tri" helps in identifying and categorizing objects or concepts that are related to the number three.

In contrast, "di" signifies two, "penta" refers to five, and "tetra" denotes four. Therefore, while those prefixes serve other numerical values, "tri" specifically denotes the quantity of three, making it the correct choice in this context.