One is often the internal representation of the Boolean constant true in computer systems. One is neither a prime number nor a composite number, but a unit, like -1 and, in the Gaussian integers, i and -i. The answer is simple, but the idea behind it is deep: 1 is not a prime number because it has only one positive divisor. Once you use the full definition of prime numbers, the confusion disappears. ONE definition: being or amounting to a single unit or individual or entire thing, item, or object rather than two or more; a single. See examples of one used in a sentence. The meaning of ONE is being a single unit or thing. How to use one in a sentence. Using One as a Pronoun: Usage Guide Explore the basic unit of math (explained by a trip to the grocery store!) and discover the many meanings of one. Lesson by Christopher Danielson, animation by TED-Ed. Explore the basic unit of math (explained by a trip to the grocery store!) and discover the many meanings of one. [Directed by Biljana Labovic, narrated by Christopher Danielson]. 1 (one, unit, unity) is a number, numeral, and grapheme. It is the first and smallest positive integer of the infinite sequence of natural numbers. 1. An indefinitely specified individual: She visited one of her cousins. 2. An unspecified individual; anyone: The older one grows the more one likes indecency (Virginia Woolf). If you say that someone or something is the one person or thing of a particular kind, you are emphasizing that they are the only person or thing of that kind. One refers to a single person or thing, as well as the number one. If you’re looking for a whole number between zero and two, you can only find one. One is all alone, but it at least it gets to be the first in line. It also gets to be the one and only, far and away the best, and one of a kind.