What is a group of 3 digits separated by commas in a multi digit number is a?

A group of three digits separated by commas in a multi-digit number is called a "thousand separator" or "thousands group." This format helps improve readability by clearly delineating different magnitude sections of the number, such as thousands, millions, and billions. For example, in the number 1,234,567,890, the commas indicate the separation of thousands, millions, and billions for easier comprehension.