What does pi mean in a circle?

Hint: Pi in a circle is the ratio of circumference and diameter of any circle. It is defined by the following equation, mathematically, $\pi=\dfrac{circumference}{diameter}$.

Complete step-by-step answer:
Basically, pi is the ratio of circumference and diameter of any circle. It means if we draw a circle with diameter 1 unit, or radius equal to 0.5 units ( may be cm or m ), then the circumference of the circle will be equal to the value of pi, which is 3.1415. So, we can define pi as the circumference divided by the diameter of any circle. The pi is represented by a symbol as $\pi $ and the value of pi is irrational which means it is non-terminating ( that does not end ) and non-repeating value( that does not repeats itself in any order ).
Generally for calculation purposes we take the value of $\pi $ as 3.14 or $\dfrac{22}{7}$ . But $\dfrac{22}{7}$ is not correct, it is only for two decimal place and $\dfrac{355}{133}$ is correct value till 6th decimal place but till date no one has calculated the exact value of $\pi $.

Note: We use pi in basic mathematics to calculate the values of circumference of circle, area of circle. Pi is also used in finding trigonometric values. Even in day-to-day life pi is used in reading behaviour of fluid ripples, designing pendulums for clocks, electrical engineers used the value of pi to solve problems related to electrical applications etc.