What is index form?

Index form is where a number is expressed using exponents - one number to the power of another.

For example, 2 x 2 x 2 x 2 x 2 is the same as 2 to the power of 5, written as 2^5. If you square a number, you write a small 2 above the number, and that is (the number)x(the number). So, it is there twice. If it was 2 x 2 x 2 x 2 x 2 there are five twos in the product, so it's 2 to the power of 5.