The smallest MEASURABLE time unit known today, 1x10^(-24) seconds. Obviously, smaller units
of time exist, but proper
equipment and methodology for measuring them
does not yet exist. Light travels 2.9979x10^(-16) meters in one yoctosecond, not the 3.33km stated above.
Learn to multiply. This isn't even an 'urban' word, so why is it defined here?