Whats the difference between using {{STATIC_URL}} and {% static %}

Whats the difference between using {{STATIC_URL}} and {% static %}

Throughout the django documentation and a lot of tutorials people seem to
pick freely between using the {% static %} tag, and using {{ STATIC_URL }}
with the correct context processor.
Can someone explain what the difference between them is, and any
advantages there might be to using on over the other.