what does PI stand for?

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:information_source: Attention Topic was automatically imported from the old Question2Answer platform.
:bust_in_silhouette: Asked By learner
:warning: Old Version Published before Godot 3 was released.

for what PI stand,

i was watching a tutorials on youtube, i seen use of this keyword something like this

set_rot(rot - PI/2)

then i see reserved keyword,
it is not from reserved keyword, so what actually this is?

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:bust_in_silhouette: Reply From: kidscancode

PI, aka Pi, is the mathematical constant defined as the ratio of a circle’s circumference to its diameter. It’s value in decimal is 3.14159265359 .

In this context, Pi is being used in a rotation using units of radians. In radians, a full circle is 2*PI, so this snippet is rotating by some angle minus PI/2 (or 90 degrees).