What is pi and what does it mean exactly?

Well it's actually spelt pi for starters. It's a constant just like every other constant in Maths and physics that's used for questions relating to any circular or spherical shape. Well just as how it'll be time consuming calculating the value of pi from scratch, the constant is already known. Pi is the ratio of a circle's circumference to it's diameter. The diameter (just in case you find this confusing) is the length of how long it'll take to go round the circle practically, and the diameter is how long it'll take to walk through it from one part of the circumference to the other while passing through the centre of the circle. It's pretty useful cause it save us the stress of measuring the circumference and the diameter of every circle we use. Also u may also be wondering why the value doesn't change for a circle of different diameter? As I mentioned since pi is a ratio that means that every circle or circular shape has the ratio, 22:7 (circumference to diameter) when simplified. I hope I could answer your question though

Pi (π) is a mathematical constant that represents the ratio of a circle's circumference to its diameter. It is an irrational number, meaning it has an infinite number of decimal places and cannot be expressed as a simple fraction. The approximate value of pi is 3.14159265359, but it has been calculated to over one trillion decimal places with the help of modern computers.

it represents mathematical constant.value is 3.14....we use this in numerical problems..

Generally pi is the ratio between the perimeter of a circle to it's diameter. Not that: this ratio is always constant and equals the well known constant pi you are asking about.