I once saw a great description of a
nanosecond (10^-9 seconds) on
PBS: a scientist held up a piece of string 11 3/4 inches long, and said, "this is how far
light travels in a nanosecond." Then she held up a huge
coil of rope and said "... and *this* is a
microsecond!"
see also: femtosecond, picosecond