An integer is any whole number, whether positive, negative, or zero. The numbers 5, 0, -3, 42, and -1,000 are all integers. The numbers 2.5, 3/4, and 0.001 are not integers because they include parts smaller than one whole unit.

Integers are complete numbers without fractional parts. When you count objects (one apple, two apples, three apples), you're using positive integers. When you measure temperature below zero or track floors below ground level, you're using negative integers.

In math class, you'll encounter integers constantly. They're the foundation for understanding more complex numbers. When you learn about number lines, integers are the tick marks you label. When you subtract a larger number from a smaller one (like 3 - 7), you get a negative integer (-4). When you divide 15 by 3, you get the integer 5, but when you divide 15 by 4, you get 3.75, which is not an integer.

Scientists and mathematicians use integers for counting discrete things: atoms in a molecule, people in a population, or whole dollars in a price. You can't have 2.3 people or -0.5 cars, which is why integers matter so much in the real world.