Factors/Divisors

If an integer is divisible by a certain number, then that certain number is a factor of that integer. For example, the integer $36$ is divisible by, in no particular order, $4$, $1$, $9$, $-6$, etc. All of those numbers are factors of $36$. Notice that negative integers can also be factors, but the GRE usually asks only about positive factors.

Another way to think about factors is, "What numbers multiply together to form an integer." For example, $5 \times 20=100$, so $5$ and $20$ are factors of $100$.