1) One trillionth of a second 2) Time unit 3) Unit of time 1) Psec 
A picosecond is an SI unit of time equal to 10−12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to 31,700 years. Multiple technical approaches achieve imaging within single digit picoseconds. For example the Streak camera or intensi...
One trillionth (10-12) of a second.
10-12 second
[n] - one trillionth of a second
picosecond A picosecond is one trillionth (10-12) of a second, or one millionth of a microsecond.
A period of time equal to 10-12 seconds. See also: Second.
noun one trillionth (10^-12) of a second; one thousandth of a nanosecond