Spin property of particles

One way of thinking of spin is to imagine the particles as little tops spinning about an axis. However, this can be misleading, because quantum mechanics tells us that the particles do not have any well-defined axis. What the spin of a particle really tells us is what the particle looks like from different directions. 

A particle of spin 0 is like a dot: it looks the same from every direction. 

A particle of spin 1 is like an arrow: it looks different from different directions.

Only if one turns it round a complete revolution does the particle look the same. 

A particle of spin 2 is like a double headed arrow: it looks the same if one turns it round half revolution. 

Similarly, higher spin particles look the same if one turns them through smaller fractions of a complete revolution. 

The remarkable fact is that there are particles that do not look the same if one turns them through just one revolution: you have to turn them through two complete revolutions! Such particles are said to have spin 1/2