In a more
physical sense, when one spills a corrosive substance onto one's
skin, causing
pain and usually a nasty
scar. Some things that will
burn you chemically: various
acids,
chlorine should probably do some damage and
lye has recently been popularized by
Fight Club. Basically anything on the extremes of the
pH scale.
I recently experienced a
mild burn on the
tips of my
fingers from
Hydrochloric Acid and it was nothing to
screw with, even on a small scale.