Safety shoes are, as the name suggests, shoes that provide safety.
They typically do this with heavy-thing-proof metal reinforcement. This covers the toes, underneath the leather of the shoes, so that if you drop anything heavy on your toes, they won't be broken by it.
Some safety shoes also have a metal plate in the sole, so that if you step on an upturned nail (i.e. stuck through a wooden plank, on a building site) it won't stab through your foot.
Safety shoes are often called for by industrial safety requirements; they can stop nasty injuries. They are also useful in bar fights, particularly if combined with a bit of Tae Kwon Do.