There are 1,000 milliseconds in a second. The prefix milli- (m-) means "one thousandth," which is 1/1,000 as a fraction or 0.001 as a decimal. Metric prefixes act as multipliers of the base unit that follows. Consequently, one millisecond equals one 1/1,000th of a second.
The second is the base unit of time in the International System. It is defined as the period of time in which the waves of radiation emitted by cesium atoms, under specified conditions, display exactly 9,192,631,770 cycles.
According to researchers at the Massachusetts Institute of Technology, the brain can identify images seen for as little as 13 milliseconds.