The document defines integers and their properties. Integers include positive numbers like 1, 2, 3, and their opposites -1, -2, -3, called negative numbers, as well as zero. The integers follow rules like -(-3) = 3, and for any integer n, n + -n = 0. Integers can be visualized on a number line with equally spaced points labeled with numbers, showing their relative positions and how they increase or decrease in the positive direction.