**Natural Numbers (N)** are Counting numbers - 1, 2, 3, 4, and so on. The smallest natural number is 1. **Whole Numbers (W)** are Natural numbers including 0 - 0, 1, 2, 3, 4 , and son on. The smallest whole number is 0.

**Integers (I)** are whole numbers including negatives of natural numbers.

Rational and Irrational numbers together constitute the system of real numbers.

**Rational Numbers (Q):** Number p/q is a rational number if p and q are integers and q ≠ 0. Every integer is a rational number but every rational number is not an integer. Every fraction is a rational number but vice-versa is not always true.

**Decimal representation of rational numbers:** Process of expressing a rational number into decimal form is to carry out the process of long division using decimal. Rational number is either a terminating decimal or a non-terminating repeating decimal.

**Irrational numbers:** A decimal expression which is neither terminating nor repeating represents an irrational number.

**Exponent:** The notation for writing the product of a number by itself several times. For example, a × a × a × a = a^{4}. Here, a is base and 4 is exponent.

**Prime factorisation:** Any natural number other than 1, can be expressed as a product of power of prime numbers.