A VERY SHORT PERIOD OF TIME' is a term used to describe an interval that lasts for only a brief moment. The acronym SEC is used to abbreviate this term and stands for 'SECOND, ' which is the smallest unit of time measured in the International System of Units. A SECOND is defined as the duration of 9, 192, 631, 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.