Factorial for a non-negative integer is the product of all positive whole numbers less than or equal to that number. Symbol for factorial is "!" and this symbol coming after a number means factorial of that number. For example - "6!" means factorial of 6.
A number factorial can be calculated by multiplying all the positive whole numbers less than equal to that number. So for calculating 6!, we have to calculate $(6 \cdot 5 \cdot 4 \cdot 3 \cdot 2 \cdot 1)$ which is 120.
Factorial Calculator (or Factorial Expressions Calculator) is an online tool to calculate factorial of a given number. It takes a number and calculates the factorial of that number on clicking solve.
Factorial for zero is 1. So, 0! = 1.
Factorial for negative numbers or decimals is not possible.