system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is particle spin? Im aware that it has nothing to do with the electron or whatever literally spinning, but that's about all I understand. What concept can it be compared to in classical mechanics?
gpt
Spin has no true comparison in classical mechanics.

It's simply a 'property' with that name.  This happens a lot - Quarks for example will be red, green or blue - but they really have no color at all.  It's just a notation for naming three different types.  They may as well have called them 1, 2, or 3 quarks.  Or apple, orange, banana quarks.  Or square, circle, triangle quarks.  Or chair, coconut, penguin quarks.  The name of the property itself is *meaningless*.

I recall a good analogy from Hawking's BHoT, involving playing cards for what you can sometimes think of spin as.

In the analogy, "spin" is a measure of symmetry, basically the number of times you need to rotate to return to the original state.  Consider a normal picture.  If you were to spin it around, it would need one full rotation to look "normal" again - so it has a spin of 1.  Imagine a playing card - perhaps a four of diamonds.  If you spin it around 180 degrees - only halfway - it now looks the same as when you started.  So it has a spin of 1/2.  Some unusual particles (like the predicted graviton) have a spin of 2 - imagine a picture that, if you rotated it around, still looked different - until you rotated it a second time.  *weird*.  

But particle physics is just plain *weird*.  Don't worry too much about it.  Classical mechanics don't apply, and analogies and comparison are always fundamentally flawed in some way.