A micro-second is a unit of time measurement that refers to one millionth of a second. However, there are other words and phrases that can be used as synonyms for this term. These include picosecond, which is even smaller than a micro-second, and nanosecond, which is equal to one billionth of a second. Other possible substitutes include momentary, fleeting, or split second. In addition, some may use the term "blink of an eye" to describe a very short period of time. Regardless of the word chosen, it is clear that these units of time represent a very small and often imperceptible portion of our daily lives.